With all due respect, why on earth would you want to do such thing? I'm not a parent myself (heck, I'm 'only' 21), but I would find it intrusive if my parents were monitoring my phone and computer activity. It's simply not their business what I do, period. Lucky enough I'd know how to avoid it they'd be monitoring me anyway.
But the idea still. It's a violation of privacy, whether your a parent or not. Just trust the kid. If you really can't, just talk with her. By monitoring her you're basically saying "I don't trust you at all."
That's my opinion tho. But I really wouldn't recommend it.