I recommend a 20 gauge for most women and even some men; it’s about 75% as potent as a 12 gauge, which should be more than enough to drop almost all perps, and the recoil is much more manageable. Get a youth model with a smaller stock, shorter barrel, and you’ll have yourself a dandy home defense gun. As for shot size, I don’t know if it matters all that much; I prefer 00 but I know some folks have penetration concerns.
“I recommend a 20 gauge for most women and even some men”
Number 3 buck is the largest shot commercially available for a 20 gauge, but should be adequate for these distances. My home gun is a 16 gauge “deer gun” with a 20 inch barrel (first round is #4, next two #1 buck, last is a slug). I have experimented with old 5 gallon plastic buckets filled with water and it is impressive.