3 month old not litter trained

[Firsttimekittenowner]

We have been debating over when to get a cat for almost two years now and tomorrow we will become cat owners which we're very excited about.
It's a long story but the owner has died. She is 14 weeks old and isn't litter trained. Will it be more difficult to train her with her being older than when they usually learn ? Any tips will be appreciated , she hasn't had the best start and we want to do everything properly! Will obviously be taking her to the vets ASAP for a check as well.

Is it that she's not had a litter tray provided for her up until now or that she isn't using it? Usually kittens and cats learn to use a litter tray instinctively.

She's had one provided but hasn't been using it. She's lived with another cat and there's only been one tray so I'm guessing this may have been the problem?

It's very unusual for them not to just naturally take to it, even if they've never been shown. If all else fails then you will need a large dog pen (sometimes the holes are too big and small cats can squeeze out - so you will need to cable tie wire mesh or similar to any holes like that). Then put in a bed and some food, and cover the rest of the floor space in litter tray/s. That way the kitten/cat will have no choice but to use a tray and will quickly (a week or so) get the idea. Alternatively if you have a very small room where you could cover the entire floor space in litter trays then that would work just as well.

When kittens leave their mothers for the first time it can be helpful to stimulate their toileting by wiping their rear ends with damp cotton wool because it mimics their mother's actions. Perhaps you could try that a couple of times after they've eaten and then stand them in the litter tray? Might be a bit odd but if they don't take to it on their own it could be worth a try?