Normally, most places give a one year warranty on parts and labor. If the exact same part they replaced in Jan is busted now, I say they should replace it free of charge. If I was the victim, I would definitely KICK HELL!
Mechanics often take advantage of women, my wife has had several separate experiences already. At least she was smart to call me from the shop before she got conned!
I suggest you bring a man with you to the shop and demand for the job to be re-done. Check and read the fine print on your job receipt, see if it mentions anything about warranty. If it does, you might want to file a complaint with the Better Business Bureau.