Let’s assume that your tortie isn't stalking you down, growling or staring at you in an aggressive way.
Like she would:
I met her this summer. Stalking, growling and staring at me? For sure.
It’s just much less common for that to happen with our cat's at home.
Let’s say she bites you, and when she does, you are like “OMG…I didn't even see that coming”. It sucks, doesn't it? You are just doing your thing, and then BAM!
How many times does that happen in life? A lot. Something happens, and you were the last to know. Because we don’t always have great situational awareness. Because we thought things were cool, but really they were not!
There is a whole situation or conversation happening, but as it happens, you are just the last to know. Bite. Ouch.
Your tortie could bite because she’s talking to you.
Maybe she is telling you she wants you start or stop doing something.
Maybe you were petting her so nicely, and then you missed the subtle signs that she didn’t want that anymore .
Maybe she has developed fear aggression.
Maybe something made her upset, and when you showed up she decided to lash out.
Sometimes they are arthritic or have some sort of injury. I once did a house call for an elderly client. Her cat suddenly starting biting and swatting her. It started when the construction started across the street and she somehow ended up with a small puncture wound.
So, most of the time, you need to get into their headspace and know what they are thinking about.
It takes a long time to learn this stuff. It’s rare for me to get bit nowadays, because I can read the behaviour of my patients.
If this is an issue you want to solve, the best way is to short-cut the process, and eliminate as much trial and error as you can, by involving someone who knows how to interpret what your cat might be saying.
I would check out www.felineminds.com