This is common behavior for a nervous cat. Unfortunately, the changes have to be made on her own and will come with time as she develops a bond and trust with you. This cannot be rushed or she will not make progress. The fact that she is willing to be around you and purr while you're sitting and calm suggests that she is going to do best in these situations, in the future, when you begin to test her boundaries. I would not do this for a few months. Eventually, move to small efforts of picking her up such as sitting on the couch with her, petting her and when she begins purring slowly moving her in a dragging motion toward your lap. Move up to sitting and slightly picking her up to put on your lap. Increase your chances of this being successful by touching her tummy while petting her and giving some 'upward' pressure briefly, as though picking her up, but not actually lifting her off of the couch. Do just enough to concern her, not scare her, and then continue with the affection. She will learn that this can be trusted as an effort from you and you should be able to work up to lifting her. You will then have to work on walking with her.
Be advised that this also may never happen. To give you an example, I have spent almost the last 2 years working with a recovering feral purebred I rescued from Texas. So far as we know, he spent the better part of 10 years on the streets. It took 6 months of him being kenneled before anyone could touch him. Eventually, he allowed being touched but did not stay for long. This eventually came to continued affection from him when handled. After 9 months with us, we finally worked to integrate him to our home. He lived under the bed for a while. We're now 1 year out from him being a house cat and 2 years out from him being in our home. I can pet him, trim his nails, bathe him slowly (though he's not happy) but being picked up still causes great panic for him. We continue our efforts in pushing his boundaries for being picked up but he is likely never going to be a cat who truly WANTS to be picked up and this is probably going to be the case for Rory, as well. What they do not learn to tolerate as a kitten or young cat can cause great anxiety for them in their adult and senior years.
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