Super irritable

I am 35 weeks and a nanny. I agreed to watch the little girl until November 15th at which point I'll be 38+5. I have a 2 year old who I can handle but this little girl is driving me nuts. She's younger so more defiant and throws food on the floor etc. I've been watching her since she was 8 weeks old so I love her and she is like a little sister to my son but I'm DONE. I don't want to stop making the money but I'm about to give them a different timeline. I'm exhausted and cranky and it's not fair to the little girl.