Sorry, Mollie, but I think your cat & abs problem is very cute!!! I have a wonderful sweet cat who insists on lying inches from me throughout my entire workouts - step, kickbox, lunges, yoga, Pilates, whatever - he won't move. I just try to step around him and try to avoid stepping on his precious tail! It's probably good for improving my co-ordination.
But, about your ab problem: can you try some basic behaviour modification techniques? Each time you find your cat acting as a pillow and grabbing you, stop your movement and move the cat away from your workout area and say "NO" firmly. It will interrupt your workouts at first, but, perhaps after getting the consistent message that her behaviour is not acceptable, she will move elsewhere? I know every cat is different but we used this technique with our cat to get him to only scratch his post and nothing else and also to curb any other behaviour that's not wanted. But, we make sure we don't occasionally reward him or let him do the behaviour. The technique seems to have worked. My cat is so finicky that if I came near him during my ab work, he'd squawk and move. I think he's paranoid someone will step on his tail!!!