OK, you have good access to the San Diego Trolley, so let's focus on things on the line that you can go to easily.
https://www.sdmts.com/schedules-real-time-maps-and-routes/trolley
I like the Old Town State Park area, which is on the green line, and also Fashion Valley mentioned earlier.
http://www.oldtownsandiego.org/
The beach area, take the Green Line to the Old Town Station and transfer to the bus system (MTS).
MTS Route 8 will take you to Belmont Park, which is a classic fun area and then the Pacific Beach Pier.
Also MTS Route 30 from Old Town will take you to La Jolla and the Birch Aquarium (Scripps) .
Something unique, but something your DD would like or not like, is the USS Midway Museum, which is a retired aircraft carrier downtown. Also nearby is the Maritime Museum, close to your Hotel.
Seaport Village is a touristy shopping area downtown that she might like near your Hotel.
That is a good set of easy access and varied things to do.