AITAH for creating boundaries w/ SD

My fiancée & I have 3 kids between us (me -2 & him 1) they’re all close in age, like I’m talking 9,8&7 about to be two 9 year olds in the home… a few weeks ago there was an incident w/ my daughter and SD about getting rid of some stuffies because they’re taking over their room. I gave them one entire day to clean their shared room and it barely got picked up, then my fiancee gave them a week, and said If it wasn’t done than we were going up there and getting rid of lots of things. It took a day and a half to go thru their entire room, fix their closet & dresser and rearrange everything to be more functional and for more storage space. All the while we got rid of 2 HUGE bags of books and half a garbage bag of stuffies to go and donate. The next time my SD went to her moms she had somehow brought up the stuffies (which was over a week later to add and she had no problem w/ anything over the week) and how now I was making her so upset and crying…. I tried reaching out to her mom via the parenting app as her and my fiancee have a PO to tell her the actual conversation and how it was said to BOTH girls, as my SD had exaggerated it beyond what actually happened. Since then my SD has been more disrespectful and talking back to me and not listening which then causes issues w/ my daughter trying to do the same and follow the older siblings… my fiancee and I had a night where it was just us and my SD after my kids’ went for their weekly overnight (SD doesn’t have one w/ her mom that’s a story for another time lol) and as soon as my kids left the car before her dad got in she immediately asked me if they were dropping me off at home, dad got in the car and she started icing me out. He ALWAYS holds my hand and moves me to a certain side of him as we walk, and she literally ran and shoved me while I was trying to catch up to him walking into dinner: then during dinner she asked for a smoothie and started to cry and whine because he said no and she needed an actual drink w/dinner. She refused to acknowledge me the entire dinner. He then took her go karting which I was already annoyed with because I hear we have no money and we haven’t done this kind of thing w/ my kids yet had $250 to blow that night on dinner, go karts and other crap she wanted…. And she proceeded to ignore me the entire time except when her dad stood by me and then she demanded his attention. Hand holding thing happened again. We got home and I fighting back tears went into my room to have a moment before having to go sit and watch a movie with them… I just wanted left alone… he comes In and asked why so I explained it all to him, and he said well what are you teaching her by not talking to her, and running in here. You’re supposed to be the bigger person…. I felt guilty so I went back to the living room, and the movie started as I’m on a completely different couch because she took my blanket and spot and he just snuggled up to her… I couldn’t help but cry and after a while I came to the room. It got so bad I was having a full on panic/anxiety attack and called my mom and she drove 45 mins to my house because I couldn’t breathe or talk and was super scared about how tight my chest was. My fiancee came in the room and said he had talked to my SD, and asked why she was doing what she was to me and she claimed to not know but knew it was mean and not right… he then told her she needed to apologize (it’s been over a month and she has YET to apologize). Since then things have just been HARD. In my previous marriage I had a SS & we had our problems but NOTHING like this. I was and still am friends w/ his mom. I’ve tried to reach out to her mom and nothing. At the beginning my SD & I had such a good relationship and now it seems it’s going downhill. We still have good moments but idk what to do. My instinct is to go in my room and take a minute so I don’t absolutely SNAP, but apparently that’s not being the bigger person….. I feel like I’m not the only one who should be held soo accountable…