As mentioned because it's a 31.8 bar you have lots of MTB stem options. Most shops will allow you to bring the bike in and mount up a new stem and go for a ride. If it's not right they'll swap the stem out for different ones until you're happy. I'd try that out first before I were to go with the adjustable option. Besides, the fixed stem will be lighter by a lot and frankly just look less kludgey.

If you go for the highest angle you can in the length she needs to fit then if it proves to come out a hair TOO high you can always shift around the spacers from below to above. And if the spacers on it now are too wide then you can switch out one of the wide spacers for multiple small ones that achieve the same stack height. So at some point it'll fit well to within a couple of mm's