Please don't feel ashamed for taking her there, in fact, you should feel very good about what you've done.
75% of the population would have probably thrown her out on the street (or ignored her if they walked by). 20% probably would have called the SPCA, where she probably would have been euthanized. And 4% of those left would have backed off when they saw those worms. LOL I give you credit!
Sometimes it's more an act of love to let go of someone because that's the best thing for them, than it is to keep them because it makes us feel better.
You wouldn't let her die, or leave her to the elements, and you didn't walk away. You found a place where she will be cared for physically, fput in a good foster home, helped to raise her babies in a safe environment, and then all will be placed in good loving forever homes where there is room for them.
The good shelters won't give cats to people who already have as many as they can handle, and it sounds like you have a full house there already. So you did the right thing. If it helps, wouldn't you like to see her in a home where she is one of only 2 or 3, where she can have lots more attention?
As as most of us learn at some point along the way, though some sadly have to learn it earlier than others, we learn that doing what makes someone we care about the happiest, doesn't always feel the best for us. That's what love, and responsibility is. And trust that she will understand that in time also.
I still feel badly for giving up my last foster back to the shelter to be put up for adoption because she was here a long time, and loved me and the other guys, and they loved her. They had to ask me to wait outside because not only was I crying my eyes out, she was howling for me.
Yet she's been adopted to a forever home (fast because she is such a sweetie -- she had more than one family wanting her). As were her babies I helped her raise -- they never made it to the shelter -- they were put in forever homes straight from my home, on New Year's Day.
And yes, I still feel guilty, but I know I did the right thing, and now I have the room and energy to help the next one they gave me.
So you should be proud, not ashamed.
I know I am nobody in the scheme of things, but for what it's worth, I don't say those kinds of things to people just to make them feel better. I say them when I believe them (maybe not how to win friends and influence people, but that's the way I am).
So again, feel proud you had the strength to do the right thing. What I find is that when I do, I'm usually rewarded by the fact that what I thought was the right thing, was the right thing.