There is a lot of good advice here. I'll toss in my $00.02
A short ski (130) is fine, however, at some point a transition to a longer ski will need to be made (150) and that can be problematic. Any ski is going to feel strange, hence, I would eliminate the ultimate transition by starting with a 150. Keep in mind it creates additional platform.
Snowdog mentioned boots. Again, almost all boots will feel horrible the first day, whether they are rental, or you take the plunge and buy. You made no mention of her weight. If she is average in that regard have a pair of heel lifts in your pocket to mitigate issues with a sore calf muscle and the boot cuff. I carry a pair in my uniform jacket and they have saved the day on many an occasion. In theory, women have a calf muscle that attaches to the heel at a lower point than men. Any shop will have heel lifts or you can make a pair.
Private or group? Some students do better in a group setting. They don't want to be in the "spotlight". Male or female instructor? Young instructor or mature? I was the first male assigned to teach full time in the Eldora woman's program. The assumption was women wanted female instructors. Turns out there are beginner women who request male instructors. They cited a variety of reasons for their gender choice.
I guess the most important thing in my mind is to find a place to learn with great beginner terrain. What is great beginner terrain? Flat, flat, flat....no crowds, no one watching, private, secluded, groomed, sunny, no wind, etc. Does such a place exist? You bet. Don't be in any sort of hurry. Lower all expectations. It would not be unusual for me to spend an entire morning doing "boot work" with a skier and then merely walking on skis to ingrain appropriate movements, balance, comfort, and confidence. Boot work is simply doing the same things one would do on skis.....without skis.