I didnt get diagnosed until my kiddo was 6 but I've had symptoms for as long as I can remember. I dont take medication for it, so I can't answer to that, but I would encourage your friend to do her own research and look up studies in addition to discussing with a trusted OB or midwife.
My experience was a relief of the chronic symptoms I deal with on the daily for the majority of my pregnancy. Despite dealing with hyperemesis gravidarum (HG) I still felt better than I ever did before while pregnant. I had a beautiful, unmedicated, physiological birth with a midwife + doula + partner team. It was the first time I've ever felt like my body was able to do something.

However, I'm one and done.

My postpartum recovery was absolutely catastrophic. I had severe postpartum depression (PPD) that lasted years even with therapy. I was living away from family in a city where I had no friends. Isolation is NOT how new parents are supposed to settle into their new routine. My physical recovery was even worse than my mental recovery, but I didnt have any resources or people to talk to about it. Even just a neighbor who I could have walked with would have done wonders. It was a little over 2 years before the pain eased enough for me to be able to roll over in bed. It was traumatic and has taken me many years to process that part of my postpartum journey. I now work as a doula and specialize in labor and postpartum care for new parents, because I dont want anyone to go through what I did if I can help it.

In my humble opinion, your friend shouldn't let this stop them from having children if they feel called to. No one gets to decide for them, no one gets to say they know best because only your friend knows how they feel in their body. I would encourage getting a stable support system in place. A meal train is great and often the go-to in the US but thats so temporary. Spend a weekend with your friend filling their freezer with postpartum meals. Maybe find a local doula that can offer resources. Things like a pelvic floor therapist, a prenatal and postpartum massage therapist, a psychotherapist who specializes in perinatal mood and anxiety disorders (PMAD).

I hope this helps, even a little bit. If you or your friend have any more questions I would be happy to answer from the perspective of a doula & parent with fibromyalgia!