This question is a trick question to see who pays attention to details. I know most people would answer the question above with words like "prostitute", "harlot" or even "sex worker". Well, answers like this would be wrong. This is what most people assume was the occupation of Mary of Egypt before her repentance. But in the Life of Mary of Egypt she specifically says:
"I was like a fire of public debauchery. And it was not for the sake of gain -- here I speak the pure truth. Often when they wished to pay me, I refused the money. I acted in this way so as to make as many men as possible to try to obtain me, doing free of charge what gave me pleasure. Do not think that I was rich and that was the reason why I did not take money. I lived by begging, often by spinning flax, but I had an insatiable desire and an irrepressible passion for lying in filth. This was life to me."
So based on the above information, her occupation, from which she made money, was begging and spinning flax. The only time we are told she may have taken money for sex was when she was on her way to Jerusalem, when she manipulated men to pay for her way there. In fact, that she had to resort to doing this, proves that she was a poor woman who made very little money. Imagine how rich she would have been if she did get paid for sex!
Below are some photos of what it may have looked like when Mary spun flax:
