Baboon bottom is often an accumulation of fluid in the tissues. This can be caused by excess oestrogen, some plants have high oestrogens and can cause this.
Usually, it shouldn't interfere with the birthing process, but sometimes they may need a hand if the swollen tissues make it hard to squeeze a lamb through, especially if first timer.
If there is discharge, and it feels like something coming, may be worth keeping a really close eye on her.
If she isn't making any progress, sometimes calcium can help, it can give tired muscles a bit of a chance to contract. If the cervix isn't opening properly, sometimes a few fingers inserted through it and gradually stretching can help to open the cervix to deliver the lamb. If you can feel the lamb through the cervix, but she isn't making progress within the next couple of hours, she may need assistance as described, or potentially a caesarian if the cervix won't open.
If lots of assistance is required, (stretching the cervix can sometimes lead to bleeding from small tears) it is worth covering the ewe with an antibiotic like a long acting tetracycline or long acting penicillin to give a couple days cover and prevent infection through bruised or damaged tissues.
she may well just pop it out when you're not looking!