I think you are 2 steps above retarded for even asking that question. You should never ask a question you don't really want to know the answer to. Also, who has sex first, and THEN goes and gets STD tested?
Anyway, I wouldn't want my daughter to have had that many partners by the age of 21, but think of it this way: teenage kids go in and out of relationships like water. 6 month-long relationships are considered "serious" to this age group, and I don't know many yong males that are willing to wait 6 months for sex when they are in a "serious relationship". If a teenage girl has one or two "serious relationships" per year, she would easily exceed the number of partners this girl has had. So is it a lot? Yes, and no.