@Addyview You've had people on here suggesting all kinds of passive aggressive tactics to use on her, mostly to amuse themselves I suspect, but it's unlikely it'll work on someone like this.
She's hard-headed, disrespectful, doesn't mind steam-rolling all over you, doesn't mind the discomfort this makes people feel as long as she gets what she wants. These people don't respond or respect boundaries or attempts to negotiate politely.
If you have a serious issue with her, then I'd basically tell her she is to stop behaving like this. She is not to ask for a SINGLE thing, from anyone - not a single leftover, sweets, somebody else's present - NOTHING. If she does, she will be either asked to leave, or at the very least, she will not be invited to the next Christmas.
Expect sulking or trying to argue with you, but don't enter into any attempts at negotiations. Say what you have to say, lay out your terms, and the stick to them.
She may be shocked at your hard response, and she may not want to go through the indignity of actually behaving, so she might uninvite herself..... which will be a win for you anyway!