No, there is no risk here.
I understand the ick factor here, but if she had an STD, it would have died long before you put it on, and because you had underwear on - even a thong - it would have protected you.
Since it was dried, everything would be dead. If it had not been dried, your underwear would have protected you. Either way, you're good.
If it helps, I would have assumed it was clean if she had pulled it out of her drawer, folded, too. I wouldn't have thought a thing about it.
But really, you're fine. :)