I really don't think that such a bold invasion of privacy can go unnoticed by her. Don't you think that since she's 18 she's capable of being responsible for her own life? I mean do you really want her to cut off all ties with you? Plus, I'm more than certain that tracking her is most likely illegal. I deeply advice you against it, it'll only lead to heart-ache and disaster.
As for the virginity thing, I don't want to tell you what to believe, but honestly, I really doubt anyone is going to hell for having sex. I mean, I'm most likely going to hell, just not for that specific reason.
Think about it, we live in a world that is capable of dealing with the consequences of sex, and since she's 18, shouldn't she have the right to choose her path for life?
Also, I feel like you're jumping to conclusions. Just because you THINK she's in love doesn't automatically mean she's having sex. Sex doesn't necessarily mean love and vice-versa.
I think you should give her some space, it's her life. That's nothing to say that it prevents you from being in it, just tracking certainly is not the way to go. If you were an 18 year old girl, would you really react so playfully had you learned that your mother had been tracking your activities? It not only creates an atmosphere of distrust, but it also makes you out to be sort of a control freak in her eyes which could potentially wreck havoc on your relationship.