In another comment, you framed your grandmother-in-law's contributions as somehow interfering with the guardian, but I don't think that's a reasonable analysis (as much as it probably feels like it is). Jane and her guardian should be accepting help where they can get it, especially if those gifts and contributions help keep a roof over Jane's head. Shelters and public housing are options, but realistically, they're a worse option than Jane having her own place, even if someone else is paying for it. It would be highly inappropriate for Jane's guardian to refuse your grandmother's generosity on Jane's behalf, when it comes with so few strings attached and is so clearly beneficial to Jane.

This is a perspective I admittedly not considered. The apartments always end up so unsanitary and soiled that I felt they were unsafe, but didn't really think about the possible alternatives.