I've walked in under an hour on the front nine at my home course, if I'm alone and no one in front of me, just over an hour on the back 9 with the same conditions. If I'm not doing some extra chipping and putting, it takes on average about 5-6 minutes a hole when by myself, I walk very fast. With a cart it would probably be under 45 minutes on the front and a little longer on the back.
Provided her parents are doing what is good for her, I say it is a good thing. She can have her parents organize everything so that the money she pays a manager stays within the family. Also, generally her parents will have her best interest in mind (though sometimes parents tend to want their children to accomplish what they couldn't in life and live vicariously through them, sometimes to their detriment) and tend to focus on the longer term good rather than the short term. Additionally living with your parents means that you have the support system in place to focus on golf only. Would a manager truly provide that. Debatable