I think I would have to ask the renter for her copy of the agreement regarding the max $25 increase, or check the file and see if you can find it. Something as important as this surely would have been documented. If no copy can be found, I hate to suggest it, but I think the renter may have misunderstood.
Otherwise, you might want to offer some information about where she can locate that type of housing. As a conventional housing provider, it may be illegal for you to treat her differently than any other renter.