After all, the Budding Green Blossom is available for purchase, and what kind of grandmother sells a gift given to her? (However, it is important to note that she does not sell this unique Green Blossom for a profit, as it is priced at 10 rather than 100 souls. Alternatively, Sirris' grandmother is already dead, and Sirris placed some flowers along with a note on her grandmother's grave, which was stolen by the Shrine Handmaid. This is further supported by the unique dialogue from Sirris after giving the Dreamchaser’s Ashes to the Shrine Handmaiden and informing her of where you found them. This seems to suggest that the Shrine Handmaid is Sirris' grandmother.
I will visit Grandfather, in the Pit of Hollows".
See a full list of her inventory below. The player is able to upgrade her stock by giving her different types of Umbral Ash scattered around Lothric.