Pregnancy Joining after pregnancy

Hi everyone, just wondering if any of ye can answer a question for me. I know you can do sw during pregnancy as long as your midwife signs off and monitors you but how soon after giving birth can you join? My friend has a 3 week old little girl and wants to join but not sure when she can? I know she can lie or not mention the baby but she'd rather not. She's not feeding her and is recovering very well from her section. Does her dr need to sign off on anything?
I've text my consultant but still waiting for her to get back to me. Thanks girls!

whenever. Midwife only signs to make sure your ok but i think thats more of if your under weight... x