Most cats will simply walk off once they have had enough attention from you. Others, however, will nip at your hand. Why do they do this? You aren't hurting her, just stroking, so it can get confusing for her.
Some cats become overstimulated quickly. The stroking gets them wound, and then the bite relieves part of that tension. Other cats just never realized that biting is inappropriate behavior. There's no consensus on strictly why some cats bite while others don't, but there are some warning signs you'll be able to seek for which will assist you to prevent being bit.
Watch your cat's tail. If the top begins twitching, this is often a sure sign the cat is getting irritated. Unlike dogs, cats don't wag their tails. Another sign to watch for is ear movement. Every cat owner is accustomed to the flattened ears of an angry cat, but it's too late, and a bite is coming by that point. Wait for the ears to begin turning to the edges. This can be a sign your furry friend is getting agitated. Stop stroking now, and you'll be able to prevent getting bit.
With cats with an inclination to bite, it's good to follow what has been dubbed the seven-stroke rule. Allow yourself to stroke your cat only seven times to begin. Then stop. This is often usually short enough to not create agitation. Eventually, you'll be able to add another stroke then another but do it slowly over time. This may give your cat time to build up to being stroked.
Even some people prefer to not be touched. Some cats also have this manner. Learning to detect the warning signs will help prevent anger on your part and irritation for your cat. This may help you and your cat to be both happier.