I have routinely done spay/abort on any feral I trapped who was safely eligible for the procedure. She has had too many litters and is fortunate to have found you to help her. I lost an untrappable feral mother years ago ( I even hired a professional trapping company) who had back to back litters. The last one presented with huge complications and she and the kittens did not make it despite my neighbors rushing her to the hospital.