You're welcome!
does she feel better after her period is over?
as for the worry, I wouldn't advise reassuring her but i can understand why you did. she's your daughter and any pain she's in must hurt to see. when we ('we' meaning those of us with OCD) seek reassurance, we're performing a compulsion because it makes us feel better about our obsessive worry.
the more you reassure someone over very small things like that, it can get worse and worse. an easy way to handle this is to refuse to reassure her. you don't have to ignore her when she asks for reassurance by any means, this kind of technique is a lot easier with support and she'll need you to help her and sit with her while she's getting those anxiety, guilt and worry spikes.
when we do compulsions, it feeds into OCD and tells our brain that it's doing a good thing by making us anxious over insignificant or irrational things, if that makes sense? when we refuse to do the compulsions, it can come with an immense amount of anxiety and panic, but it's very temporary and it's advised that you sit through the spikes and allow the feeling to pass while practicing calming techniques. the more you resist compulsions, the less and less you feel the need to do them.
i would definitely talk to your daughter about doing this before you do it though, just so you can see how she would feel about trying it.
so, an example (since i feel like my words are a bit jumbled :L):
your daughter comes to you saying she's worried that she hurt her brother when she cleaned his ears. instead of telling her she did/didn't, a good thing to say is: "I don't think reassurance is going to help you so I'm not going to give it to you right now" and then try to sit with and comfort her until she calms down.
it's important to do this with her consent, and when it involves little irrational things like this. i wouldn't do this with bigger, more reasonable and important worries.
i would advise googling more about reassurance seeking since i don't think i explained all of this very well, but that's where you should start looking