Hi Sharon,
I can see your dilemna. On the one hand you want to think well of someone and happily re-home a cat; on the other hand, what is there to stop it happening again and will you be creating suffering for the cat?
One consideration is to ask this lady a lot of pertinent questions, preferrably face to face in her home, which would test her sense of cat care and responsibility and give you an idea of lifestyle, etc. taht the cat would have to endure. I would say that you were assessing the type of cat which might suit her and her family lifestyle. I would add that you would need to see if you had such a cat.
I would trust your gut feeling which I think comes over as extreme caution. You say that this was an 18 month old unspayed cat with no insurance. She works full time - lno different from most people- but couldn't take time out to take the cat to the vet on a regular basis, if necessary. It poses the question of 'can't' or 'won't'. Are the hours of the veterinary surgery so limited to make it impossible for full time workers to get to? Either way a cat is unlikely to have proper care for problems; I wouldn't be surprised if the cat had no vaccinations, chip or ID as well. I think the answer lies in those facts.
My own feeling is like Mark and not to re-home a cat to her. It seems her cat is way down the list of importance in her lifestyle and wouldn't get much attention - be it health wise or probably attention wise. Her loss is sadly regretted and, it would seem, outside her control but I wouldn't trust her to look after another cat any better.
I know that you will be the first to agree, a cat's welfare comes first before all other considerations.