How does her mother imagine her future? Does your SD go to school? Does she have any plans? Does she have any ambition at all?

Does your wife understand that she is enabling her daughter to NOT live a normal life?

Your wife is the problem here, not the "loser" father or SD. She's enabling SD to not function normally and actively preventing her from getting better. Put your energy on your wife's poor parenting. 

I'm sure there are "swipes" back and forth about this issue.  But have you and your wife sat down quietly and discussed your concern about SD59's apparent depression and any future plans?  Does she see SD launching at some point or does she see her staying there permanently?    As aggravating as I, like you, would find this situation, if you can summon up the patience to hear what your wife says without criticism, it will give you an indication of what's next.

Please do come back and let us know how you get on.  Just remember there are no quick fixes.  Everyone is going to have to learn new ways of behaving and this takes time.

I'm imagining myself in your wife's situation.  I'm seeing my daughter look so sad but I don't know what to do.  I see my DH being exasperated but I feel protective toward my fragile daughter.  I'd like to think that my daughter will launch into a happy life but I have no idea how that would happen.  I dont know what to do and I worry all the time.    I'm feeling sad, worried, confused and scared.

I am going thru all this to help you adjust your attitude as you speak with your wife.  If it were me, I'd welcome a concerned conversation, no accusations, a chance to voice my concerns, a feeling that someone is sharing my load and helping me see some options.  Good luck.

JRI you generally give wonderful well thought out advice. However, I disagree with your take on things for this original poster. His wife is an enabler and his SD, despite her mental issues sounds like a manipulative user.

Original poster said

If she does something careless in the house it's me that get portreyed as the "ogre" by my partner, her BM because I made her 'feel bad'.

 

Original poster's parner doesn't seem to care about how this situation is affecting him. Sounds like she is playing victim as well. Original poster's partner should have already been taking on a major role helping her daughter with this situation and working on her daughter gaining life skills so she can be prepared to launch.Original poster's partner sounds like a lazy parent and she should be trying to minimize the negative impact her daughter is having not only on herself, but her partner and the rest of the family.

Original poster also said

SD is almost an elective mute with me and her mother. 

However, in her room on calls with friends she has the best time laughing hilariously. So much fun! 

The original poster's SD may very well be depressed, but sounds like she is also using her depression as a crutch. She can't do things adults do, but she can be on the phone with friends laughing  hilariously and having fun? I personally wouldn't tolerate her behavior. There would be no talking on the phone laughing hilariously if she doesn't help with chores, cooking, etc. For some people with mental issues, having a job, even if only part-time helps them immensely. That would definitely be in the plan. She is 18, and an adult, so she definitely needs to be in therapy working on managing her depression so she can eventually launch into adulthood.  

Original poster, I do also want to say that the way you feel is not unreasonable at all. No way would I let my partner make me feel like an "ogre" for calling out her daughter's crappy behavior. If she did her job as a parent, you wouldn't have to.Smh

It is so unfortunate that people like your partner think someone is going to coddle their kids or adult kids forever. If people like her want to coddle their adult kids forever, then they really should be with someone who feels the same way they do. Or better yet, stay with their kids other biological parent. Or better yet, they could also opt to stay single.

Is it really that hard for parents to realize that their adult kids have to grow up and launch? In a step situation it should be a requirement imho.

I think we can all agree Other Dad has reason for concern, not only about SD but for his aggravating situation.  We see it as his wife's issue since we all know it never works for the SP to take the lead.  I think tbe therapy suggestion is great, not just for SD but also his wife.  Opening up communication about the topic is crucial.  Good luck, Other Dad, please let us know how it goes.

I'm going to play devil's advocate. My DDstb21 had a rough time during her teen years. She was depressed and anxious, which is fine because I can support her in addressing that, but she was not allowed to use it to buy out of life. I fell for it for a while by rescuing DD and cooing her thinking that I was emotionally soothing her and nurturing her, but she really wasn't improving and she wasn't resolving any of her own problems, including ones she caused through self sabotage. When I noticed that DD would pull the "anxiety" and "depression" card to justify her fuck-ups in life or to avoid being addressed for anything, I realized that I was doing too much and allowing way too much. I had to change my parenting and require that DD go to counselling.

DH and I went to counselling to learn how to parent DD and one of the things that our therapist said was to not just let DD continue being the anxious and depressed mess that she is. We were no longer to enable her and we had to teach her to fight for her way in life. There's a lot more, but the gist of it is that I think your DW is enabling your SD. Your SD will not ever grow or change for the better. The world out there isn't going to require everyone to tip-toe around her and not say anything lest they'll upset the delicate one. It just doesn't work that way. Your SD needs counselling, but so does your DW. Your DW's enabling of your SD is negatively impacting you and your marriage. That's why you're unhappy and frustrated.

Sure your SD is broken, there also may be some using her depression and anxiety to bow out of life and stay safe. There's nothing wrong with being depressed and anxious, but there's a lot of resources available these days to help a person help themselves. 

By the way, the minute DH and I stopped enabling our DD, she completely changed and is very independent, capable and fierce. She resolves her own problems when she has any, but she rarely does because she doesn't self sabotage anymore in order to use it to bow out of life. DH and I couldn't be more proud. 

Maybe insist on getting your DW into marital counselling or maybe take charge and insist on counselling for SD. Nothing changes if nothing changes. Let your DW know that what's been going on is negatively impacting you and your marriage and you will no longer stand for it. Something must be done. It's your marriage being affected, so you have every right to stand up and say something and insist on change.