Feet on sofas

I’m puzzled how you have a friend who comes to your home with dirty feet and skid marks on her slippers 😱

I put my feet up on my own sofa, not with shoes on though, and I would never ever do it in someone elses home,

I think your friend is disgusting and lacking in basic manners. I have my feet up on my sofa now, if I went to a friends house it would not enter my head, its basic manners and showing respect for someone else's home.

I'd never out my feet on my own or anyone else's sofa with shoes or slippers on but can't see why a close friend would object to bare feet or socks.
Next time the OP's friend visits, why not say (politely) you've had the sofa steam-cleaned and would like to keep it clean so she must please remove her footwear.

Either put a throw on the sofa or when she's lying out pop an old hand towel or similar under her feet, and tell her to use that every time. Chuck it away when she goes.

Just as we put covers on our sofas when our DC were small, I would put a cover on before she comes.
I'm sorry you have to put up with her inconsiderate behaviour.

I don’t know if there’s an easy answer to the feet on the sofa years ago when I visited my sister in Georgia I put my handbag on her countertop and she simply picked it up and said handbags don’t live here I’ve never forgotten it so truthfully I think you have to let her know that feet don’t go on sofas and you have to accept that she probably will have some hurt feelings about it but that’s really OK because it’s her stuff

I always put my feet up on my own sofa, but would probably not do so on someone else's. I wear indoor shoes and don't give a thought to any dirt on the soles. My furniture is for comfort, not show.

I won't give this a second thought, just they were comfortable in my surroundings, but if I saw something on the sole of her slippers I was say something to her.

I’d put a throw on the sofa before she comes.