You have a couple of ways to go here. If you're keeping her as an indoor/outdoor cat, let her keep going outside if that is her preference. Be happy you don't have to deal with a smelly litter box. She won't stay out long with kittens to take care of. She'll train the babies herself, and very quickly normally. For them you might want a litter box.
If you're turning her into a strictly indoor cat, which is a lot safer for her, then try different brands of litter. If she doesn't take to the box, and "goes" somewhere in the house, put the litter box in that spot. She should get the idea.
When kittens are old enough to start eating on their own, showing an interest in Mom's food, I used to wean them with a mixture of high protein baby cereal (human baby, not kitten food) with chicken broth. This is gentle on their systems and inexpensive. They'll love it. Add in a bit of kitten chow gradually and you won't have kitten digestive upset.
For now, let her keep them in the dark until their eyes are open for a few days.
Do not declaw her, even if you're keeping her strictly indoors. A cat who has been used to roaming will find a way to get out, and she would be totally defenseless against dogs and other predators without front claws.
Please get her spayed after she's weaned the kittens. That will save a lot of trouble. She won't go into heat while she's nursing these, but you would know if she did. She would yowl loudly to be let out. You can't mistake it for anything else!
Good luck, and enjoy the kittens when they get old enough to play.