There is no hard and fast rule. Generally, you have to give the person a reasonable time to recover them and written notice to do so. If she does not get them by the 15th, send her another another, sent some way or ways you can prove delivery, reiterating how long she has left her belongings there, when she was supposed to retrieve them, prior attempts to get her to take them, and that you did not agree and have not agreed to hold them indefinitely. In the notice, given her another 30 days to recover them and state plainly that if she does not get them by then, you will consider them abandoned and put them out for disposal. Then if she doesn't get them by then, set out them after the deadline.