No doubt you have little ab strength- 4 surgeries! Don't feel too bad if you can't do too much. I would suggest as Almeeker & Lizzycritter to just do some simple not overly intense exercises,at a slow pace and listen to your body.Too sore, painful? Take it easier next day.or use easier exercise.Crunches,Reverse crunches, even just flattening your back while on the ground etc. I assume your fully healed,that you can do planks is a pretty good sign.Trying to do hanging leg raises with little ab control and strength would be no more than an exercise in frustration and possible further muscle pulls injuries.
I think if you are regular you will likely see results fairly fast perhaps weeks, although with your injuries your full potential may take a while. Google " thinking mans guide to ab training" by Ian King,very good over all advice progession on ab work. Just as applicable for women which I am assuming you are.