My mum does it.
It's basically down to her personal taste and what she thinks is "right". I like coloured sheets, she thinks white are "cleaner". When I moved into my house she replaced all my coloured sheets (and towels) with white ones, and took mine home to use as scrap fabric.
She also has bought me cutlery. Two sets. She believes in "best" and everyday stuff. She's cross I put one set in the loft as I just don't need it.
I don't like clutter. She buys me lamps, knick knacks, etc. if offended if I don't want them, then complains I'm a hoarder and the house is cluttered.
She honestly, genuinely thinks she's helping. She'll rearrange everything when she visits, because she needs to clean, or it looks better over there. I tell her not to, but she worries about not helping out. It takes me a week to get my house under control after a weekend visit.
So I don't really have an answer. Some people do have a strong sense of what is "best" and any other way of doing it is wrong.
Does she have a key to your house? I'd take that off her to start...