if there is any risk of HIV if a person fingering a aids infected woman and have a sore from nail biting, the sore means no blood but ripping of the skin from the corner of the nail like that of hangnails.
Though the possibility is very small, it is not zero. The virus is transmitted, usually, by blood to blood contact. Though some other bodily fluids can transmit the virus also. Not all exposures result in infection. And the virus really isn't that easy to transmit.
You should speak with your physician, or one of the community HIV clinics, if you are concerned.