The very best answer is to let her choose. Point her to
The Cornered Cat as was previously suggested, that will put her on the right course.
A safe suggestion, for several reasons, is a 3" or 4" S&W K frame revolver. .38 Spl is fine, but of course there's nothing wrong with .357 Mag. One nice thing about the K frames is that there are so many options available in grips, hence she can get her revolver and then get grips to fit her hands. That, and the manual of arms is so simple.
FWIW, SWMBO (who has rheumatoid arthritis) ended up choosing a 4" S&W model 15, a K frame in .38 Spl. Yeah, I found it for her, but then again she tried it out herself, liked it, and bought it herself. The grips fit her, the gun is a delight to shoot and is a tack driver. Unlike your friend's wife, SWMBO prefers to use her revolver in single action mode. She insists on cocking the hammer. Yes, I know -- I've told her time and again that it is supposed to be used as a double action. She nods, and cocks the hammer anyway. She claims that she doesn't have the strength in her finger for the DA trigger (which happens to be nice and light). Whatever. She's comfortable doing it that way. At least she's armed.
I suggest for home protection a S&W model 10 or model 64. The 64 being stainless.
Those are nice, but don't turn her away from the corresponding adjustable sight models. Those would be the models 15 (which is at SWMBO's side of the bed) and 67, respectively. While the fixed sight versions are faster out of the holster, it doesn't make all that much difference as a HD firearm. Likewise, don't turn her away from the .357 Mag versions of all of the above. After all, you don't have to shoot .357 Mag ammo in a .357 Mag revolver, .38 Spl works fine in them if she is recoil shy.