What is incumbent upon one who swore not to cut her hair at a specific hairdresser, then did so?

It is permissible for a woman to cut her hair, provided that it does not involve imitation of men, or disbelieving women, or immoral women. You must offer an expiation for breaking your oath, which is feeding ten poor persons, or clothing them, or freeing a slave. If you are unable to do so, then fasting for three days, as Allah the Almighty says: "Allah will not impose blame upon you for what is unintentional in your oaths, but He will impose blame upon you for what you intended of oaths. So its expiation is the feeding of ten needy people from the average of that which you feed your [own] families or clothing them or the freeing of a slave. But whoever cannot find [or afford it] - then a fast of three days. That is the expiation for oaths when you have sworn. And guard your oaths. Thus does Allah make clear to you His verses that you may be grateful."