Dog won't stop licking and biting

My dog has recently become extremely itchy. So much so that even if you pat her above her tail she starts kicking because it feels good. I have no clue why this has started because her sister is having absolutely no problems at all, just her. She's starting to lick and bite her fur off of her butt/thigh from bothering the area so much. The only thing I noticed is small spots here and there with scabs. I assumed it's just from her irritating the skin, but I'm not 100% sure on that. My MIL and husband are saying that it's not fleas because her sister isn't itchy like she is, but I don't know. This is the best picture I could get of the red spots where the scabs are.