I echo what everyone is saying. I played an instrument through college and my wife was an accomplished pianist who taught privately for years, so we've been in a different position than you. Even so, private lessons for my daughter (violin), were super important and helpful. Newsflash- kids don't like to learn from their parents. My son wasn't quite as interested, so school class was sufficient.
If she's in a school program, and you end up getting private lessons, I wouldn't worry about addressing theory separately. That'll come.
Beyond that, I encourage you (well everyone), to have multiple instruments in the house- accessible and even on display if possible. They don't need to be high end, and you shouldn't attach any expectations to them- just have them there. The musically curious will gravitate to them. For us that meant guitars, ukuleles, trombone, keyboard, violin, and some percussive instruments. Now deeper in high school, my kids have each shifted to the choir from their primary instruments, but it's not unusual at all to hear a guitar being played in a room by my daughter, or seeing my son banging keys figuring out a popular song.