I finally trapped her. Four of her kittens from previous litters were taken in by the Nine Lives Foundation in Redwood City, CA. for permanent homes. I've been really concerned about not being able to trap her to be spayed and vaccinated before her next litter of kittens. She's not very old and this is a viscous cycle for her to be on.
It can be frustrating trapping because it can take months to trap some cats. But the end result is worth it! Fewer homeless kittens and healthier adult cats. Fighting decreases and overall health improves.