Step parent advice please!!!!

Okay so my husband has 3 kids...
7,6,4.. His oldest is his daughter.. The boys are great, I love all of his children like my own. Well about a month ago his daughter started asking to stay with her mom more and more on the days we have her (which is just Friday, Saturday, and half of Sunday)... So her mom finally tells her she needs to spend time with us and she has been crying for her mom all day, saying she thinks we are mean ( me, husband, and my daughter who isn't even here the days they are here she's with her dad)
I've never once been mean to this girl, and her daddy is such a kind man. I don't know how to deal with this situation. I've offered her hugs, girls dates, lay with me and watch girly movies, everything. I just let her know I'm there without forcing myself on her... It's been two years, and she's just now having these issues. We used to be really close and this is crushing us both... She's already in counseling. I'm at a loss... Has anyone else experienced this? Any and all advice would be appreciated.