Hi and welcome to TCS.
That was great of you to take in this kitty and I do think she is pregnant.
Are you at home with your parents? You said your little brother named her, so I assume you are at home with parents. Can they take her to the vets, or you if you aren't as young as I was assuming. They can give you an idea of how far along she is, because by the looks of the pics, I would say yes, she is pregnant. I would say further along as well, so she must have come to you that way, and I appreciate you taking her in while she is pregnant and getting her and her kittens off the street. It looks as though she has started to clean the hair from around the nipples to make it easier for kittens to nurse, they do that late in the pregnancy, in the last 3 weeks or so. Can you feel them moving? You can usually feel them in the last 2 weeks of pregnancy. Cats typically carry for 63-67 days, about 9 1/2 weeks or so. In some pics she looks to be around 4 weeks and in some more and others less, so it is hard to tell by pics. but, you can see that she is clearing the hair, like I said, which makes me think she may be around 6 or 7 weeks, but a vet can give you a better idea of when she will be due, and how many, by feeling them. I think she looks to be young, most definately under a year, and she can have problems with delivering. So you want to be sure to keep an eye on her and have vets and emergency vets number on hand in case of problems, I would also make sure to be signed in here at the time of delivery too, LOL there are lots of expirienced peple here that can help you through it and let you know what's normal and not, and what to do if it's not, and most of all support you and talk you through it!
If she is under 4 weeks when you bring her to the vets, the vet may be able to preform a spay/abort, it isn't as bad as it sounds and will not effect the mother, it could be the best thing for her, especially if she is young, but she looks like she may be too far for that and you may not be comfortable with it either, and that is understandable. Good luck with Blacka and keep us informed on how she is doing and post pics of her babies when she has them!
If you can check out the forums, there are lots of posts and links to kitten care that you may find use ful, just ask some one if you can't find them some one would be happy to post them for you, I can't remember them and can never find any thing I am looking for.