I'd send her back. Sounds like the director handled it appropriately.
5 year old kids are curious and as long as the staff knows these 2 boys are curious, they will be on the lookout. The bathroom thing, that sounds like nothing, I wouldn't even think about that one again (and my DD gets crazy gusher bloody noses too! )
I would be concerned if the director did nothing...I mean, if she said "oh, kids exaggerate" or "are you SURE that happened" or "thanks, I'll talk to the staff"....but the director had a meeting to discuss it with the staff, THEN came and told you about it afterward, so she followed through. I'd move on.
Similar thing happened to DD when she was 7. New after school program, there was a special needs boy and she said he touched her privates. I talked to the director, who sort of rolled her eyes and said "really? are you SURE? I'll look into it" After I talked DH off the ledge, DS10 chimed in that they were playing tag and yes, the boy touched her there, but it was really as she ran by and it was like he was tagging her. Oh, OK, we thought, and moved on. Except the director never got back to me. So about 3 days later, DD tells me (and DS corroborates) that the boy has been LICKING her, on her face. Apparently, he mouths and licks things and the staff knows about it (yep, they just put the toys in the bins each night, don't bleach them...so nasty). This boy is physically 10 or 11. I go right to the director and tell her that is unacceptable, that the staff needs to make sure it doesn't happen again. She says "well, DD should stay away from him". I flip out, and say "that's the plan? SHE should stay away from HIM? He follows her around! Where is the staff" and the director says "well, they are watching the other children. We have to treat this boy the same as all the other children. He deserves the same care as your DD and we can't tell him he can't play with certain children".
We pulled our kids out that very day. Because the staff and director were completely unconcerned with the sanitation, the fact that licking could escalate, that is was GROSS, and that this boy, with very many special needs, did not need any extra supervision or accommodation. Or that is was somehow my DD7's responsibility to make sure she didn't get licked by a larger boy.
Go with your gut. If you feel the director handled it, then put it out of your mind. If you feel like you got blown off, then pull her out.