I've recommended the Surface in many forms to many people, non of them have been particularly tech savvy and all have gotten on fine with them, mobile worker using it to replace a laptop, window fitter who had had enough with Apple products, student who wanted a tablet and so on, they have all been fine with them.
Horses for courses though, why did she say she wanted an MBA, is there some software that she wants to run or some other reason for looking at the MBA?
If shes going to be sat at it for a while then a 13" over the 10" will make a difference, I'm fine with mine but I have an external monitor so its not so much of an issue, that said I'll most likely be getting a Pro3 so 12" is much more usable so perhaps waiting for the Pro3 might be an idea for her also, it wouldnt hurt to go into somewhere like PCW or John Lewis or whoever else local to you stocks them, see if she thinks she can get on with the OS and how things work, if the size of the screen is a stumbling block for her then tell her that a 12" version is on the way...