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.