Another option is that it's very possible you could fit a 7 speed freewheel with the Tourney RDER and keep the friction shifter.
That would give her a couple more usable gears.
One problem with 5 speed is the large steps from 3-4-5.

Some of this is dependent on frame/axle spacing & possible redishing of the wheel.
IF you have a co-op, These issues could be addressed relatively inexpensively + you could do a bit of other maintenance such as servicing the wheel bearings at the same time.