Since she is new to you and your home, it will take her a while to get comfortable and settle down. It may take a while since she is so old and set in her ways, and she may not be used to getting brushed. Also, some cats don't like getting brushed a lot. One of my cats loves being pet but will literally sprint away from me when I have a brush on my hand. He's getting better, and this will take time, but it is worth persevering because it helps their coat so much and keeps shredding down.
You may want to invest in a zoom groom (only $8 or so at petco), which is a rubber tool with thick rubber "bristles" and it has the highest success rate on pets who normally hate being brushed, at least the ones I hear about on this site. My cat will run up against it and basically brush himself because he likes it.
