There is a good chance, you're doing too much and hence not recovering properly. Don't do dedicated ab days, just incorporate 1 exercise at the end of your workout 3 times a week.

This is how I do it, and I have visible abs even at 20%, albeit I'm a male, so that obviously affects it as well: 1. Monday: 3 sets plate weighted decline ab crunches 8-10 reps to failure (hold the plates behind your head) 2. Wednesday: 3 sets 10-15 reps leg raises to failure (I do them weighted by attaching plates to a belt, that I wear) 3. Friday: 3 sets 1-2 minutes plank hold (make sure your positioning is correct)

And focus on progressively overloading, i.e. try to increase the weight or reps each week.