Hi there, LactMed and InfantRisk are two resources that have been indispensable to me in my 4 years of breastfeeding! (I'm new so I don't know that I can post links but they're easy to find on google and are so helpful!)
In my experience, many medical professionals are pretty uninformed when it comes to lactation in general and often defer to the "abundance of caution" type of advice which can be so frustrating. I was repeatedly advised to pump and dump for what I knew to be no reason at all, or to wean, in order to go on different medication(s) when it'd be even more stressful and inconvenient to do so! All it took was a quick phone call to InfantRisk with my surgeon/doctor in the room and I could nurse on without worry.. Each medication and situation has its own risk/benefit analysis to be undertaken of course, but there are also emotional, mental and physical affects of weaning, even if one WANTS to wean, so it should be done gradually. I know I felt a relapse of lots of my symptoms of anxiety/depression/OCD and ptsd (or maybe delayed PPD??) once I weaned my toddler son, even though I wanted to, and even though I was still nursing his baby sister around the clock. My body was used to a certain level of oxytocin etc. that was "patching me up" emotionally without me even realizing it. No one warned me about that possibility!
Hope this will help your friend!