Yes it is slut shaming, because you concluded that she must have uncontrollable sexual urges based on the most ludicrous reasons. About a teenager! For you it's THE ONLY EXPLANATION POSSIBLE. "Ew, she must like sex real bad, she can't help but think about big penises all day long!"
Do you think just because she is a teenager she doesnt have a nymphomaniac? Bro you have phone, you can educate yourself. Those, the word you just said, is from your brain. Its projecting all the stereotype and prejudice against women. Fuck off. I just said nymphomaniac and then you are the one who gave the meaning in one sntence that I said. Just fuck off. Ew