I am so, so sorry to hear about Tooties babies. How awful for you and your roomate to have to see this. About 2-3 years ago, our shoemaker took in a stray mama that had 5 adorable babies and after 2 weeks they started to die off one by one. All 5 of her babies died within 2-3 weeks. I asked my vet what could have happened and he said it's hard to say without doing test on them, but if he had to make a guess, he said it could have been from distemper.
If you plan on still feeding the mama and taking care of her as an outdoor cat, please bring her to be checked out by a vet and get her spayed before she becomes pregnant again. I'm sure you wouldn't want to go through this again.

{{{{{{{HUGS}}}}}}} to you and your roomate.