If the aim is to have a single chainring up front, 10 speed would give her a good range of gear without having a large jump between each cog.
e.g.
11-34 with a 44t chainring, 32-100GI.
If she need a lower gearing, a 11-36 with a 42t cassette would work for the majority of ride, I would not recommend a wide 8 speed transmission as the jump is far greater with a 11-32.
If the aim is to have a single chainring up front, 10 speed would give her a good range of gear without having a large jump between each cog.
e.g.
11-34 with a 44t chainring, 32-100GI.
If she need a lower gearing, a 11-36 with a 42t cassette would work for the majority of ride, I would not recommend a wide 8 speed transmission as the jump is far greater with a 11-32.