Hello and welcome to the Asylum...
Physical size (height & weight) is not all that relevant when choosing a defensive handgun caliber. You need to try the most common and popular defensive calibers, in guns that feel good in your hand... for both you and your significant other
Try your favorite guns in 9mm, .40S&W and .45ACP. They all have different recoil "feels"... in the same gun model, many will prefer one caliber over the other. You may be surprised what you discover.