It looks like she scratched herself because it was/is itchy, it often happens when a rabbit has mites and this is a typical spot for them as well. If you never had experience with mites I would visit your vet or at least would contact them online sending some clear photo so they could confirm and prescribe a treatment for it. Scab itself is not dangerous just she will continue scratching herself it it is itchy so you'd need to define what is causing this.