I'll add one more to the pot. NAA makes a .32ACP Gurardian, which is a double action all stainless semi automatic. It is much smaller than a Glock 26 and would only weigh a couple more ounces. But in my opinion 6+1 of .32ACP is far greater than 6+1 of .22LR or .25ACP. It is blowback so it will kick a bit harder than the Keltec, but not much more than a G26 I would imagine.
I think the Walthers are sharp looking little buggers, but it has been my experience that small .22LR autos have extraction issues, especially with the cheap ammo. I have only found CCI Stingers to be reliable in a lot of these small platforms. So if you do go with the Walther give that ammo a shot if you can get your hands on it and have her practice mag dump drills to test the feeding and also since that is probably how a .22LR will be employed (which you cannot do with the mini revolvers).
The Seecamp, Guardian or Keltec would be my first recommendation, especially if this is going to be her primary carry and not a backup gun (I didn't catch it if you mentioned that).
The mini revolvers will not jump out of your hand if you put rubber grips or oversized grips on them, which I have done (rubber) with both of mine (.22LR model and .22WMR). The rubber grips allow you to hold onto the small gripping area just fine especially since the rounds are such light cartridges. The little mini revolvers make ok backups, or snake guns loaded with shot, but other than that they are a curiosity and should not be used as a primary defense in my opinion.
As others, I would recommend the .25ACP over .22LR, especially if this is to be a primary carry. The semi-rimmed cartridge extracts more reliably, centerfire ignites more reliably and as stated above FMJ is decent for penetration as well as having a slightly larger bullet (50 grains usually).
If you go .22LR or .25ACP I would recommend FMJ however, not just because of penetration, but due to loss of mass in such small rounds (shedding as well as fpe on target).
Good luck with it whatever you decide and know this: Pictures are mandatory! We will all want to see what you decided on.