What gun she's going to carry is the least of your worries (within reason--like no Desert Eagles
).
You should be much more concerned about HOW she's going to carry, at least if she wants to dress like a women, or at least the women I know (if you'll please excuse my gender stereotyping!).
I've helped a few women figure out their carry problems and it's not an easy proposition.
In general, IWB or OWB behind the hip carry is difficult for women because a) they are short waisted and the butt tends to ride up into their underarms which is uncomfortable and makes the draw difficult, and b) they have to wear concealing garments that overly restrict their fashion options. That said, this could work if the weapon was relatively small like a mini-Glock, Keltec, Kahr, etc. and your friend doesn't mind (or perhaps normally) wears loose sweaters, fleeces, sweatshirts, jackets, etc.
The short waist problem can be mitigated to a certain extent by moving IWB or OWB holster to in front of the hip (so called "appendix carry"). This is not cross draw. Some rearward cant in the holster is also helpful. Again a concealing garment must be worn, which may or may not be your friend's style. This is a very overlooked carry method and does not represent a significant departure from the position of her duty weapon. However, if the women is big busted or very short waisted the butt of the weapon can ride up into the underside of her breast in a sitting position, again uncomfortable.
If she's going to wear concealment for a shoulder holster that same concealment will generally work for both methods above depending on the size of the weapon. Skirts are going to be a problem with little support for a holster. Dresses are right out. If she's the skirt-suit type a shoulder holster is not a bad proposition, don't overlook it. However, as you rightly point out, it causes a training issue, but this can be overcome with, duh, training! Live fire training can be a range safety issue since there are muzzle sweep issues associated with realistic shoulder holster training (the shoulder holster "pirouette" they make you use on many ranges is a pain in the ass and not very realistic). You may need to find some private range time.
Pocket carry is also generally a problem for women as their fashions either have no pockets or the pockets are somewhat vestigial or the pants are fitted close the body.
Small-of-back carry can offer better concealment but it can be hard to get to, uncomfortable, and possibly hurtful if you fall on it.
Pouches are a consideration, but they are not very popular these days.
If she never wears dresses or skirts perhaps an ankle holster, but if her calves are small in diameter as they are for many women it can be difficult to get a secure fit.
All of the above issues have driven most of the women I know who carry to off-the-body solutions, i.e. purse carry. Yes, yes, this is completely substandard to on-the-body carry, but when women want to wear skirts, dresses, tight fitting clothing, etc. it's pretty much all they've got left.
Mrs. aa777888's solution is a Keltec P3AT in a Kydex pocket hoster she has custom affixed to the inside of her fashion purse. Rarely she'll wear it in appendix carry in a Kydex paddle holster but it's usually winter and a lot of fleece is involved
A close female friend of the family has chosen a G27 in a G&G holster purse.
These days, with so many excellent medium to very small pistols and revolvers, just remember it's less about the gun and more about how it's carried. If it's not comfortable it's not going to be carried. This is especially true if there's no motivation, i.e. no duty to, or not a warrior/sheepdog type.
aa