SD. She's 17. And a sophomore in high school. She will probably be living with us FOREVER. She's as lazy as can be, but I'm told all teens are.... however, my 14 year old DD is plenty able and helpful. 
I have tried to like SD. She's not a bad kid. My 9 year old son likes her and she's very nice to him. She's just not a pretty kid. Horrible posture. Horrible teeth (has braces and needed procedure after procedure to get teeth to descend at 15, and to get them straightened out - with lack of compliance on her end). She also gets gingivitis frequently Bc she doesn't brush well (she didn't know you had to brush the back ones TOO! I know she's not that smart- but that blew my mind!) She lets her arm pit hairs and leg hairs  grow out even though I buy her the best razors and encourage good hygiene. She was quite stinky, too, until I got her clinical deodorant. She had her period in the bed one night and stained the sheets - sleeping in them for 3 more nights until I mentioned it. Her IQ is lower. Probably in the 80s. (Below 70'is considered mentally retarded.) However, I feel like she's more lazy than "slow". My DH said "let's get married. Things will be easier on you." Well, in some ways, yes. In the area of kids - I feel like I gained an Extra responsibility- more than my 2 kids put together- and they are younger. My DH doesn't always make excuses for her, but he tolerates more than I would in the area of laziness. He says "let her fail. We have told her over and over again. She will have to learn the hard way." 
 She puts about 60 hrs on her phone a week. She has a learners permit but won't learn to drive. All of the financial responsibilities fall on us - and I'm the breadwinner. He also pays $470 in child support to BM. She's not much of a help in raising this kid. She likes to be her friend- and only parents SD when it's convenient. I was the one who noticed she had certain issues with her GI system. I noticed when she had anemia. I got her a math tutor. I finally got my DH and her Mom to see that SD couldn't write a paragraph or a paper, much less (that took 2 years of convincing)... and got her help for that. Of course DH or BM don't stay on top of the extra writing help. If I mention it I feel like a nag, so I shut up. The kid says she wants to go to college, but honestly, she will fail out the first semester. I am willing to help her, but nobody else -including SD- wants to put in any work towards the endeavor, so I say SCREW IT. Not my sh!t show to manage. 

If I get her something special that I think she'd like - she doesn't use it (like the Apple Watch sitting on her night stand)....

I'm just exhausted by this kid. And I know I have it better than most.... but it's still my reality.