Just my opinion...
Due to stature, strength and training time limitations I would rule out semi auto pistols. Likely trouble racking the slide and handguns are the most difficult of the weapons listed to master without moderate practice and training.
Revolver...difficult to master without moderate training and range time.
Rifle...any that are suitable for home defense would be expensive and I think for most folks they are overkill for true home defense. Also manual of arms might be more involved than a beginner should try to tackle under stress.
Shotgun...pump 12 or 20 ga would be my suggestion. Easy to use and fairly simple. Would still need some training about how to load and unload safely and how to leave it ready but unchambered with kids around. It might push her around due to her size but with some training on proper technique she should be able to handle it.
IDPA Member A00640
Founding Charter Member - Middle Tennessee Shooter's Club