Never - not so much for what she'll get away with now - it's pretty easy to keep tabs on a 7-year-old but because it will set a precedent that will be hard to reverse when she is older and has lots and lots to hide.
We have a family laptop that all 4 of our kids share. The younger boys (6 & 8) don't know their password and have to have my husband or I log them into the computer. Parental controls limit what they can do. My two 14-year-olds have their own accounts, but parental controls limit when they can log in (from 3-9 PM), what they can do, and sends me a weekly report of all of their activities (when they were on, what applications they used, what web sites the visited or were blocked from, what they searched for). This laptop is stored by our desk in the family room and can be used in the family room, at the kitchen table or, for school work, in the room that the two older kids share where there is no privacy anywhere.
I have a friend who has older kids and even when they all had their own laptops, they were not used in the bedrooms and we don't bring our computers in the bedroom either. Nor do we have TVs in any room.
At her age, I would recommend having a computer that she is allowed to access, but put parental controls on it and do not have it in her room. It should be something that is used only in the presence of others.