The Pixel 3a is a better phone than either of those two, if you can get over the fact that you don't like the way it looks. It will also get all the latest security and OS updates immediately and runs clean android, which is a pretty big deal IMHO.
Between the P20 lite and G7 Play, the P20L has slightly better hardware in some areas but the G7 Play is probably going to be updated more regularly on the software side. The G7 has a much better processor, at least according to Geekbench (I'm actually questioning the P20L's single core results as they are worse by a factor of ~6). Reviews on the G7 are very positive relative to the price (you can by it outright for about $250). The G7 is a 2019 phone the P20 lite is a 2018 phone - I am not sure what OS the P20 Lite is running currently but it launched on Android 8.0 (10.0 is live right now on all the Pixels). There's a tiny chance Huawei's political issues cause problems with support, but unlikely.
Given her basic usage, it sounds like any of these phones would be OK but if you want the best phone out of those few, the 3a is the one to go with especially if you have to stick with it for 2 years. And you get almost all of Google's fancy camera tricks as it seems like you might want a good camera - the camera on the 3a is hugely better than the other 2 options, particularly outside of ideal conditions.
Reviews on the 3a are overhwlemingly positive:
https://www.tomsguide.com/us/google-...view-6452.html
https://www.theverge.com/2019/5/7/18...atures-io-2019
From the iVerge review
"In 15 years of reviewing phones, I am not sure if I’ve ever been able to write the following sentence: a $400 phone has a camera that’s among the best you can get on any smartphone."
Just my $0.02.