I have slightly inverted nipples and have had no major issues with breastfeeding. I would suggest your friend at least try if she wants to breastfeed - maybe contact the ABA for support and make sure her attachment is as good as she can get it too. Maybe her GP was just trying to stop her getting too stressed if she can't BF, in which case she could just ignore the advice if she feels confident to give it a go anyway? I'm sure that if there is a real problem with her feeding she will know about it well before it harms the baby!