Dunno. Gilmour has several children and there is a daughter who is known to play guitar. But this picture seems to have appeared circa September 5, 2020 and first appears on pintrest and imagur which suggests to me Photoshop. If it were real I would have expected to find it in other places as well.
It is posted here with an April 2020 date and in a context where it seems like Romany Rose Gilmour's mother is having some fun so it probably is real enough to have been posed, not Photoshopped.