Thank you Exile, I appreciate the suggestions. The browser add on (Chrome) is what she installed at first and then later their phone app (Android). And I did in fact have to untangle it from Google sync (it kept reinstalling itself) too which was a pain but eventually I made sure it was removed from her profile. When I check her devices I look at the history to see if anything was installed and I jump into "Developer Mode" to do an update to see if it brings anything down from her syned profile. I'll keep in mind the flash drive. I haven't noticed her having one, but doesn't hurt to keep an eye out.
Regarding the modem, I'll check into them. For the router, I'm using Eero and they claim that they are working on a blacklist function to deliver later this year, but I'm getting tired of waiting so I may end up dropping and getting something with better security features or adding Circle to the mix. OpenDNS is a stop gap but it's easy to get around it. My daughter has shown herself to be a lot more tech savvy than I expected!
I'll consider your suggestion about consulting a removal specialist. You have been very helpful. Thank you!