Nanny help

So we have a nanny and I was just curious what other people think in this situation. She is a really nice girl, 23 years old and in college online full time. She works for us 4 days a week from 7-4. We have 3 kids - 6 year old girl and twin 2 year old boys. The oldest is in school full time and the nanny handles pick up and drop offs. Her primary responsibility is the twins. The scenario- the boys play very very well together independently. We don’t limit tv time and have let her know this. Every day she does an activity like baking with them, taking them to the park, a science experiment or something along those lines. But then she sits down on the couch and lets them independently play with the tv on for about an hour while she eats and does school work (the twins do not nap anymore). She’s always in the playroom with the kids and she safely monitors them and she provides them snacks but I’m not sure if this is considered lazy nannying. We have a camera and she knows about it but we haven’t said anything so I think she thinks we’re ok with it. The boys play really well together but I feel like she should be playing with them at all times. I don’t want to fire her because the kids all really like her and every Friday she voluntarily vacuums, mops and does the kids laundry. (I don’t make her do this before anyone says anything!!). I just don’t know if I should talk to her and tell her I don’t feel comfortable with them playing independently for an hour a day while she does her work and is on her phone. We are paying her fairly and I don’t want to lose out on money for the hour she isn’t directly playing with them. What should I do? What would you do? Would you be upset as well?