How to encourage using the litter tray

[FromLittleAcornsGrow]

We’ve just adopted a 6 year old cat from friends who are splitting up.
cat has always been an outdoor cat and will eventually be here but I need to keep her in for a bit so she doesn’t try to get back to her old home or worse run away/get lost.
normally the cat would have gone outside to pee and poo.
obviously I need her to use a litter tray here until I can start letting her out but she won’t even entertain it! She’s already Pooh’d on the floor.
is a cat that’s 6 too old to retrain to use a litter tray?
any advice anyone?

Never to old to learn. Just gotta follow them around when they show they need to do their business scoop them up pop them in the litter box, reward with treats if they use it.

memycats
I tried this but she fights me when I pick her up and jumps straight back out of litter tray.
I will keep trying.