frustrated step mom

my oldest step daughter is  13,, she was always with us ,,over for weekends ,school breaks ,,summer  vacation. . her mom gets child support but ,sd gets taken care of when she is with us too,,her mom got used to  asking  my husband for every little  thing ,,,which is fine ,but she get c.s ....he finally  started saying he couldn't do certain things, bm  got to were she slowly  started picking fights and refused to answer  calls and back then my sd was only 9 years old so it was easy to poison her..... sd  now says stuff to  us like - we care more for my kids than her ,,,or she says things to her dad ,my husband ,,like  ,,I only want just us to go do something ,,or even that the other kids aren't her siblings ,,don't bring them around. 

when we got engaged  ,,we asked b.m if sd  could be in the wedding ,,of course she refused, ,and we were never able to  actually  ask sd ..... we got married  without her in it ,despite our best efforts ... my sd  came for a weekend  and noticed the wedding pictures and says ,, why couldn't I have been in the wedding ?? we quickly told her the truth, that we tried and her mom wouldn't let us. . 

she currently has the worse attitude towards my husband -her dad ... and he just takes it... but I'm over here like ,,nope ,,I'm done, because - it seems like she is convinced we are the problem ...