I'm actually looking to get the same board. I'm 4'10, 105ish pounds and an instructor as well. For her size and ability level, anything higher than a 138 would be pretty difficult to use. The Onyx has a lot of new tech from the men's line this year, and from what I understand it can be used for both freestyle and all mountain riding. I currently ride a 136 Rossi Tesla, and even though I ride almost every day anything larger than that is going to be difficult to get a diverse use from. The board itself generally requires a good amount of maintenance, so if she goes go for something with a sintered base make sure that you're willing to do the upkeep.