I was in this position! I was recently caring for 4 1/2 yrs old twins and they had a rough start! The boy threw violent tantrums while the girl cried for her Mommy all day! The tantrums were quickly nipped in the bud, and the little boy got on wonderfully, but the girl just wouldn't quit. After a month and a half (I started with comforting her, then moved to removing her from the group when she started up) she was still incredibly disruptive and if I"m being honest incredibly annoying! At 4 1/2, you're not a baby anymore and there are better ways to voice your feelings than crying ALL DAY. She missed out on a lot of fun! After 2 months, I was at my wits end and the group couldn't handle it anymore either...even her brother! So, I discussed it withthe parents and they decided to have Grandma watch them instead. A huge change in the atmosphere, let me tell you!! So, I totally get how you're feeling....and if the other ladies suggestions don't work for this little one, then you shouldn't feel guilty at all for saying goodbye!