For introductory caliber, it's hard to go wrong with a 22LR. Very little recoil and inexpensive ammo to practice and just have fun. I don't think I've ever seen anybody who didn't enjoy shooting a 22 and it's a great gun for training.

For the CCW part, you might consider having her shoot a few different calibers (22Mag, 25, 380 and 9mm) to see what caliber she feels comfortable shooting. I've had to train several women in LE and all of them were able to shoot a 40S&W with training. Some preferred the 40 and some preferred a 9mm which has a little less perceived recoil. There's obviously a difference in terminal ballistics between these calibers but she has to be willing to shoot the gun for it to be useful in a CCW incident.

On a side note, it would be a wise idea for her to have at least fired YOUR CCW gun a few times in case you get injured and she needs to use YOUR CCW gun to defend both of you. I hope it never happens but it's always wise to be prepared.

Once you know what caliber, you will probably end up with more than 1 pistol, depending on seasonal clothing (heavier in winter and lighter in summer), what method she's going to carry concealed (in her purse, on the belt, gun bag, etc.). Like most of us, she will probably find that she just prefers one pistol more than the others and uses that one the most. On the plus side, you will get to buy and shoot more guns.