I have also been stopped by her a few times in the last 18 months and asked for money, however she has never been agressive when I have declined and just walks off. I have a feeling she may be staying at the Honor Lea hostel on Brockley Rise, see link below. They state on the website below that they do not accept "People with current substance misuse problems who are not actively engaging in support/treatment. or Those with recurring problems with violence" so maybe she is having treatment there...perhaps if anyone has a problem this could be raised with them.
http://homelesslondon.org/details.asp?id=HO231