advice on durable smart phone?

[testcase]

Many (Most?) Android based phones have accessible batteries so, a dead / low battery can be swapped out with a charged spare. As mentioned, have chargers at home, work in the car etc. If GF is truly as hard on phones as you indicate, I'd stay with a much less expensive Android based model that can be replaced as needed. If you do get her onto iOS, perhaps buy it at a vendor like Best Buy and, get their extended warranty that will cover hard use.