And there is another story in the Paterikon about a prostitute in Alexandria giving much of her income to the poor. When som over curious and zealous monks asked Avva Pimen (IIRC) what to make of that (quoting the OT where it was forbidden to receive a whore's gift/money), Pimen answered along these lines: She doesn't remain in debauchery/prostitution, for the fruits of righteousness are seen in her."
Is this the whole context of the episode? I'm confused as to how a practicing prostitute can be called "righteous" just because she gives to the Church (I'm reminded of mobsters in the US who give a lot to the RCC). I know one can point to the example of Rehab, but do we have any indication she kept being a prostitute after she went with the Israelites? I don't think so. To be perfectly honest, my "earning salvation" alarms are going off .
I'm aware that in ancient times, women's options were very limited, so perhaps the woman in this example was constrained into prostitution by economic necessity?
There is a story in Benedicta Ward's book "harlots of the desert" about St. Thalis and St. Paphnutius. I've seen it in another version about St. Paisea and St. John the Short (I think, if I remember right). I'm not sure who the original figures are or where the mix up is, but the story sounds so familiar that I wonder if it is the source of what you are mentioning, but a little bit confused or rearranged. I'll put a brief summary from memory as a possible context, though I'm sure someone more knowledgable will tell me I'm confused.
A woman was a wealthy widow with much property. She give liberally to the poor, holding dinners for them and giving alms, until she was financially ruined. In desperation, she eventually either turned her home into a house of prostitution, or herself became a prostitute, possibly to feed herself and her household, and possibly out of a misguided desire to continue to supply the needs of the poor. News of this came to a near-by monastery, one where many of the fathers had received hospitality from her before her ruin. One of the fathers (possibly her uncle) was told the news. He went to her at her home, and rebuked her. She was filled with shame and asked how she might be saved. He told her to go with him to a convent and spend the rest of her life in tears that she might be saved. Immediately she want with him into the desert. The pushed on hard, until she was exhausted late in the night. He went off a ways apart, and they slept. In the morning he found her dead, and wept bitterly that she had perished so close to a life of repentance. It was revealed to him by God that her repentance had been accepted, and he gave thanks. As such this woman is considered a saint.
Don't know if this is a related story or just a similar one, and I can't remember which account exactly of the ones I've seen was the right one... but in any case, a story like this is a much more likely explanation for how a wealthy prostitute could be considered a saint than just giving money to the church.