My female cat (domestic) has suddenly acquired a white bald streak on the top of her head. On the skin is extremely small red dots almost like blisters. However only 3 or 4 are on it. I doubt she is stressed because it would be too hard for her to clean up there and she doesn't go outside. Does anyone know what else it could be?

It could be a fungus of some kind like ringworm. Th e best thing to do is get a vet to look at it and if they feel it deemed necessary, they will culture it /do testing accordingly.
In the mean time its proabaly a good idea to keep from touching it just in case. If it is ringworm or scabbies, its zoonotic meaning it can be transferred to humans.
Good luck!