I plan on keeping my young daughter from accepting a gift from my son's girlfriend.
Is there a reason why you do not want her to accept the gift?
It's too expensive.
I think that's acceptable. Why don't you speak with your son's girlfriend about getting a more acceptable gift? It would hurt your daughter to see the gift and then have it taken away.
I don't care what my daughter feels. I'm her mother and I can't let her accept more expensive gifts.
May just be a good idea to have a discussion about it. It kind of stinks to not give the gift to your daughter if your son's girlfriend meant for her to have it. In the end, it is ultimately your decision to decide on what to do though.