Hi Trish! Welcome to YT! How sweet of you to rescue that sweet baby and you're doing the right thing by just giving her space and letting her warm up at her own pace. Unfortunately, shelter babies come with all types of unwanted behaviors but with patience, positive reinforcement & consistency, she'll adapt disciplines the way you want her to.
One of my girls is like that...does not like going out in the rain(or right after either) or walking on wet grass. On those days, I sometimes had to pick her up and put her in a spot in the middle of the grass, not too close to the door to run back in. As she would walk to get out of the grass back onto the sidewalk, etc. she would just eventually go ahead and pee. Not right away..it took some time before she would do it but now she knows..even if it has rained and/or the grass is wet, when she's outside that means go potty & then she can go right back in.
Also, all my girls are trained to use both pp pads & go outside. Now they'd rather go outside & will not use the pads freely, but on bad rainy days/snow, etc. they know they can use the pads as an option. You should still try your best to stay consistent & teach her to use it outside also but there are other options.
So you're not the only one with that problem.
Hopefully, she will get it in time.
Best of Luck to you! Would love to see pics of your baby also!