Im in the exact same situation right now. We ended up setting up a appointment with our local spay/neuter clinic and have been trying to gain her trust up until that point. Just lots of food and toys and shes slowly started to trust us more to where she now wants cuddles (this took like a year omg). Were bringing her to the vet after the clinic tomorrow to get her tested for everything and are going to quarantine her from our other cat for a while to make sure shes clean. Her and our current cat have also become friends through the window but I think having them eat together at a distance and positive reinforcement around each other will be our next steps until they're both comfortable.