Jamie,
My daughter is also same size as your young lady
she cant reach to 'paddle' my bike about, nor could she with my M750ie.
However, with my cut down seat, it is just a possibility, but she isnt too happy, as she can only 'dab' on one side or the other!
All the monsters with the later frames - the 888 ones, will be too tall, without mods - or a nice Ohlins which you can adjust the ride hieght with - just like Fatbloke in the UKMOC does (he is a short-arse too
)
Becca neatly fits all the older bikes, including the m900, as they are all so much more adjustable on the loop arm.
Good luck,
C