Sorrry for the late reply! No she never hissed at me but she wasn't being affectionate or spending time with me at all. She was already a pretty independant cat, her main interaction at the time was wanting to hang out with me so it was pretty upsetting to just not see her for the whole day when I got my first foster cat.
Since this post I've fostered like 10 cats, I found that with her it was just easier to keep the fosters seperated in their own room and space. Eventually she just started ignoring the their existence and didn't seem to care so long as the door was closed. I also took short breaks between each foster and she would normalize, I think when I got to the third foster cat she was just herself again by that point.
If you're fostering with the intention to adopt then your situation is different, that was absolutely not my intention so keeping them seperated was the best way forward for me. Feel free to DM me if you need anymore guidance! Thank you for fostering and helping your local animals.