The advice others gave you is great. If she's letting you pet her, over time, see if you can pick her up. If she lets you, a vet visit would certainly be a good thing. And neutering her after the kittens are weaned (as well as neutering the kittens) would be great.
We've always had barn cats, and they often end up being house cats. Luckily, my 5 dogs love cats. right now we have 2 house cats (both former barn cats) and 2 barn cats.