You'll find some excellent accessibility advice, information and photos here:
It won't be straightforward: Rome's pavements are often narrow, crowded and uneven, sometimes cobbled....access to and getting around the ancient sites is not easy...but it is by no means impossible to see large parts of the city. It just requires a bit of extra muscle at times, a willingness to adapt plans and a bit of forward planning where possible. For example, you can easily see the outside of the Colosseum and get reasonable views of the ancient forum from the wide, 'modern' pavements/sidewalks in that area.
Central historical Rome is (as well as being absolutely wonderful) compact and very walkable: I'm certain you and your daughter will be able to explore large parts of it without too much hassle.
Just one additional note here as Leics has provided good information: one of the more challenging aspects of Rome is that many of the restrooms in restaurants are located in the basements and have no lifts. Others have doorways too small to accommodate a chair (although it sounds as if she can walk a little?)
I would just be mindful of that and be sure to have her use the facilities at the hotel before going out for the day, and making use of those at larger museums and other attractions where accessibility is not as challenging.