I don't think it'll be a problem because Herpes is a common disease, and if they were screening for it, they'd have to deny about 40-50% of American applicants. I haven't heard of that happening, so I don't think it's the case.
Also it's not a degenerative disease, and it doesn't cost a lot to treat an outbreak.
Lastly, some medical conditions that would disqualify the sponsor are waived in dependents. So really I think you have nothing to worry about.
I am agree with thaiguy, it should not be a problem, not at all, just make sure your daughter is under medical treatment ASAP (If she is not already) so you can prove it to the Doctor (medicals one) as a plus in case he/she asks for .