Been there!  My DH was a horrible mean person because he started to push back on her ridiculous demands. She went crying to BM about it and spun stories. BM took a 13 yo's word hook, line, sinker and dismissed DH's categorically. It was the beginning of the final PAS stage before she never came back to our home.

I coudn't do anything and stayed out of it unless she made a demand of me I couldn't or wouldn't agree to.

Ahhh.. the old playing the parents against each other ploy.. most kids do or try it.. it's exceptionally difficult to deal with in a divorce situation when the parents don't communicate.

Spawn would do this to her parents as well.  She would tell DH negative things about Meth Mouth and vice versa.  My DH would feed into it because he thought that if Spawn was talking bad about her mom then she must be on “his side”.  I finally had to point out to him that this is what Spawn did so that she could play both sides to get exactly what she wanted out of each of them.  DH never believed me and to this day when he had talked to Spawn when she tells him bad stuff about her mom he takes it as validation that Spawn might be on his side…really sad.

bad mouth them and we did not bad mouth them to SS.

As nauseating as it was to speak of them with SS without rancor, we made sure to support SS, let him express his heart break and confusion, while keeping him within bounds of speaking of them respectfully.

We were always careful to not vent about them within earshot of SS even when he was very young. Or so we thought. When he was a toddler and becoming conversant and we were learning to blend and first learning to deal with their toxicity as we were forming, storming, and norming our blended family and marriage, DickHead called to cry to DW, profess his love, and how much he missed his family.

DW guffawed when she answered the phone and DipShitiot sobbed his pathetic crap.  She told him the conversation was over and asked  "Do you want to speak to your son?".  She activated the speaker phone and called to SS and told him it was "Daddy (FirstName)".

SS in a happy toddler voice said "Hi DaddyDIckHead!".  DW and I gagged back shock. 

Dickhead popped back at SS "What did you say?!!!!!:  DW hit the mute button and corrected SS.  Then unmuted and asked DickHead what his question was that the connection was bad.  SS then said "Hi Daddy (FirstName)" wich fortunately does sound a bit like "DickHead".

We were careful to not speak like that around SS. But... kids are smart and the young ones pick up on things.  We never again used anything but their names when speaking of anyone in the SpermClan again while SS was in the house. Not when he was watching cartoons, or asleep. Never.  He was young enough that he apparently did not remember that incident.

When SS would return from a SpermLand visitation we would talk about his trip, how that part of his family was doing, what he/they had done while he was there visiting, etc..... It would take a few days for the details of the trip to come out.  Usually when they had been manipulative, guilted him about something he had or was doing at home that they did not do or get to do, etc...

For DW and for me, it was not about hearing how much SS hated them and enjoyed his real life with us. It was about raising him to be respectful and learning the crap they were giving him when he was in SpermLand.

Even now, we discuss them with SS-31 in a respecful manner.  He knows they are shit, he has learned that for himself.

Though I still get a chuckle out of the "Hi Daddy DickHead!!!" memory.

I think all kids complain about their parents or step parents 

Ngl it's sometime amusing to hear how they spin it and of course they're always the victims

One day I heard dudes daughter complaining about ME lol

In the beginning of our relationship (after I first moved in together) this lackidaisical parenting dude kept dumping his kids off on me/leaving them here while I was here. 
 

Not only did I not like it but his daughter didn't nor did his exwife who told him she didn't want another woman around her kids. (In my mind I'm like girl no worries I'd rather you keep your kids with you then) 

One day it was his parenting weekend and he decided to up and leave me with his kids

well, She called her beastly meddling remote stalking mother and complained that she was home alone with the "evil step mother" who then called that dude and complained like a disgruntled Karen customer on hold for 32 minutes and 4 transfers with AT&T

Well needless to say I refuse to be left alone with those skids 1. It's not my parenting time and they care less about seeing me 2. I'm not risking false allegations 3. If something happened to them while I'm alone with them I really don't want to be legally responsible 

I'd make it a point in future asks.

Skidlet: "Daddy will you buy me x,y,z???" 

Dad/SM: "Not until you do the things I asked you for help w/. I don't want you complaining to your mom that I refuse to do/buy anything for you so I'll make sure I let her know exactly why I said "not until"". 

She will stutter, sputter then go "oh shit!" in her head. 

My name for it is "Playing the Houses Against Each Other:, sort of a riff off the GOT Houses.

I saw that with BOTH SD24 Feral Forger AND SD17 Powersulk. Mainly Powersulk, who is really great at gaining sympathy using the Victimology Method. She would get in trouble with Husband when he was actually trying to parent her, and she would either call her mother, or cry to me. Or when it was visitation, go cry to BM Toxic Troll. 

When shed get into trouble with Toxic Troll, she would cry to Husband or myself (Im always included, but secondary). She was very careful and subtle about it. And of course each House was eager to hear the bad about the other. Especially bad things about me. Causing TT to gleefully send toxic texts to Husband. When it was turned around, it was Husband swooping in to rescue poor abused child. Or tiptoeing around the TT.

With FF, she was the "boomerang child", when issues arose, she wasnt parented, she was bumped off to the other household.

I noticed the word "For" rather than "with". Your SD doesnt want her father to do "with" she wants the "for". A BIG difference.

When my SD21 was younger, about 6-7 y/o, she used to play my DH and I against each other. I saw through her, but it took DH a little longer and then he nipped it quickly! She was caught standing in the doorway smiling/laughing when she got my DH and I into an argument and I pointed it out to him. 

I don't have much advice for you on this, unless you can talk to your DH and have him nip it at your house that is. Call her out on her sh*t and see if that makes a difference.