it took me 8 weeks to notice a difference.
i do want to point a couple of things out though.
if she is not comfortable on her saddle, it could severely cut short the amount of time she is able to ride.
also, if the saddle is uncomfortable she will subconsciously unweight herself slightly off it by supporting some of her weight on both legs at all times. which means she is doing more work to go the same speed because her pushing leg is also having to overcome weight of her non pushing leg.
ie. if she is able to consciously unweight the non pushing leg, she will be able to go faster at the same level of work.
changing my saddle to the correct one allowed me to go faster and ride longer and be more comfortable.
in addition, bike fit in general is a big thing. i raised my handle bars thinking it would help my back, but it made it worse. so i slammed it and it got better .
raising the seat heat to a correct height has helped me generate a bit more power and also better for the knees.
finally, is she working on cadence? i know that when i was mashing gears instead of spinning, the perceived level of exertion was a lot higher.
here are some things i would look at.