If you can ask them in person once you get back from break with at least a week or more to ask another person, I would meet them in person ASAP. Otherwise, I would ask someone else, just in case.
This person might just be a procrastinator. I had someone wait to write my letter until right before the deadline. Some LOR writers are known for this...but on the off chance this isn't the case, you're better off with a back up.
It's definitely a super rude thing to do if they don't write your letter. Sorry about your situation.