Helping Peppermint Patty

We adopted Peppermint Patty from The Humane Society a few months back. We love her. She is 8 years old. Since adopting her she has been sick most the time. We've had two vet visits and one ER. She cannot kick URI. She stuffers from asthma and a heart murmur that we know of.  She is in a state of constant wheezing most the time. There are underlying issues why she's staying sick. Finding the issues is taking money we do not have. I've exceeded credit funds on her. I do not want to take her back if I do not have to. So, I'll try this. Asking for help. Can you help us please?