I would just talk to your kids about the whole santa thing,and remind them that it is a pretend activity many families play with young children,but your family does not. I find it rather sad that some feel the holidays can not be *special* without the lie of santa. I wonder how the kids at my childrens school feel;the kids who do not celebrate something during December.
My ds was recently put on the spot at his school because the majority of kids(6-9) are santa believers,and they could not get over the fact that my ds was not.They told him santa would die if he did not believe in him.Told him santa IS real because the teachers believe in santa. Lol, I even had a mom call and complain to me,and the principal pull me aside and BOTH say I needed to talk to ds,because his non-believing was causing issues for the other kids.Essentially ds was *ruinning* christmas for other little kids by not believing. LOL. I don't see why parents did not talk to THEIR kids and tell them some kids don't celebrate the holidays with a visit from santa.No,unfortunately it is up to me and my kids to preserve the myth for others regardless of what we celebrate.
I would get the doll if you think she really wants it,and put another gift away for a birthday.I was going to say the inlaws should buy it,but that will just keep this santa issue going,and that is not want you want. The holidays can be special without all the pretending. I would be making sure the kids knew mom and dad bought the gifts not santa,but no need to do that on christmas day.My kiddos asked for a few things,and I told them I would buy what I can.They know our funds are limited.
I would probably have a talk with the inlaws too(privately) and remind them that santa is not done in your home.Skip the santa mall visits too.