I had a cat once that I thought was going to give birth for what seemed like forever. I had a birthing place ready for her 3 weeks before she actually gave birth. She ended up looking like a walking football, and when she laid down, it looked like she had a soccer match going on in her belly. She was fine, and only had two kittens. Some cats just show earlier and more than others. So, I wouldn't worry too much, but you should take her to the vet to make sure she's healthy and the kittens are healthy. Especially if her first litter died.
Please think about getting her spayed after this litter. Is your cat an indoor/outdoor cat? If so, she will have litter after litter if not spayed, and that is not good for her. It wears her out too much and can cause serious health problems.
But, good luck, and like I said, don't worry a lot. Make sure she has someplace quiet to go. If she wants you there, she will come and get you. I had another cat that did that...I put her in a quiet place in another room, but she kept running out to get me and I had to sit beside her the whole time. But, most prefer to be alone.