I am in love with my F122. The layout is perfect (except that I would prefer having no keypad) with no modification required.
The only thing you need with a F122 is to make a Soarer converter and while not that easy the first time you do it, it's not that hard to do if you take the time to follow the instructions and ask for help.
Also, since the F122 has an AT connexion, you can probably use some kind of active converter to make it work if you don't want to build a Soarer converter. But the Soarer will let you remap all the key to you're liking and that's a BIG plus if you want to use this keyboard. Sometimes remapping 1-2 keys can make a HUGE difference.
As for the price, your biggest problem will be the time since it's possible to find one under 100$ shipped if you are patient and somewhat lucky. But since it's for her birthday, it could be harder.
And if you set your mind on the model F, the AT model F layout is nice also, but it does not have the more standard modifiers and while it's possible to change it for a more modern layout, it takes more manual skills while the F122 already has a very nice layout as is.
So I can't compare my F to an M since I have not been using an M for 15+ years, but from what I remember I didn't like the M so much (but I was younger) while the model F is a dream to type on. It feels smooth, light, crisp, springy clicky all of this at the same time. For typing it's just perfect in my opinion. And it's built like a tank.