I am aware that this might be a late answer for this year, but still, I will make an attempt.
You tell about the friend:
- "she is a very sweet girl"
- "I normally do not mind having her around"
- "I'm just kind of torn"
- "she doesn't really have a family to spend time with"
Although "she is very disruptive in the family", she is not a complete disaster. Combine this with the facts that:
- Easter is just one time per year;
- Easter is about us being reborn as newer better selves.
So having her around might be the better choice, instead of rejecting her.
I do not know why she does not have a family to spend time with. Because she relocated for some reason? Maybe she does not have a family left?
For two years, I live in a foreign country, with no family. For some reason, I seem to be unable to make new friends, so I spend most of the time alone (except some interactions at job, or other minor interaction in private life). I am usually a listener, on the introvert side. But when I catch somebody to talk to, I tend to become a defective unstoppable talking machine. It is just a reflex of my mind. Sometimes I become aware of this, but usually only after the other person really heard a lot from me.
So, as a longer-term solution, you might want to get to know this friend better, help her get her life settled better somehow, and things might solve by themselves. She will become even sweeter maybe.
She invited herself.
The friend self-invited herself.
What did you answer? If you accepted (even silently), for whatever reason, it is most polite to go along with your (unfortunate) acceptance. Especially since it is not just any day / evening, but a major social / religious event.
You have to be aware that it is not really possible / acceptable to ask for thinking time in such cases: "I will tell you in X days if I accept you".
So if you did not reject the self-invitation from the very beginning, it is too late now.
How do I politely tell my daughter-in-law not to bring her?
There are no right words. It will put you in a bad light in front of your daughter (in front of the friend also, probably), and it will put your daughter in a bad light in front of the friend also.