Can my dog be mentally challenged?

My puppy will be a year old next month but she lays at my feet every time I come near her with her feet in the air. She also goes ballistic whenever anyone comes close to the yard and only allows a few people to touch her (she has repeatedly bitten my husband). She was from a large litter and was picked on by the others but has never been mistreated since I have had her. What can I do to socialize her better or could she be mentally challenged and this is the best I can hope for? Dolly has really grown on me. I am very attached to her and give her lots of love.