I feel for you. At one point we just had to put our foot down with our son. I felt bad doing it (still do from time to time), but his father told me one day "You want our children to be treated fairly, so you'll need to stand by that and treat them all fairly. He can have special treatment from time to time, but he needs to realize that he can't always have it his way. If you're constantly allowing him to have it his way, then he'll never learn, and that will be on you. That's not fair to him to never know that reality." As we progressed with, in lack of better words, "putting our foot down" a little at a time, he's learned and grew so much, he just blossomed up and knows hard limits, like throwing a temper tantrum will not get his way, but "using his words" just might do the trick, and sometimes he just shrugs it off when we say "No. Not right now" or "You can't have it... it's either dangerous, or not yours, or not your turn" or "It's either mommy's or daddy's or sisters' or brother's rest time right now..." etc.

I also like Amanda's #3 comment (all of them good), but specifically #3 because I sometimes use those tricks (modified or not) on ALL of my kids, and sometimes my husband too (LOL). Works for all honestly.

It's important to have a support group by your side and those that have your daughters best interest at heart. People that are rude or for whatever reason are unkind do not deserve your daughters love they will be the ones missing out on the amazingness of your child. Remember your her voice and she is going to have to deal with people that don't understand her for the rest of her life, but how you handle it will teach her how to handle as time goes on. God bless!

Sounds like seperation anxiety. Because your inlaws have been removed from the picture she thinks that anyone can be removed on a. Whim.
1 even if it makes you uncomfortable to do it. Take her back to see herother grandma. We see my husbands dads family once in a great while he was never a good dad but made early attempts at being a better grandpa. Exposure to their grandchild may make her realize what she is missing out on.
2 give your mom and sis space to recouperate. If this means taking that week off your work or school or finding a temporay daycare then it may not be feasable in the neerterm but it sounds like they need a break. Most areas do have respite care try using that.
3 YOUR CHILD IS NOT A DOG..... however try looking up solutions that work for pets. Many of these stratagies can be modified to work on humans too