There are pros and cons to becoming a mother at any age, and it's sensible to consider them.
However, I do agree that one of those factors that few seem to seriously consider is that biology can't be changed by desire. Also it's NOT just conceiving that can be difficult.
I have endo, I knew from a young age that "something" was wrong but was repeatedly fobbed off.
Getting pregnant wasn't difficult, my first pregnancy was accidental on the pill used correctly at 18...and ended in mc. The next 2 pregnancies I conceived in less than 3 months.
Before ttc with ex husband I had to delay 3 times for medical reasons. 2 infections, 1 the treatment for which was contraindicated with pregnancy, another the condition itself needed to be out my system at least 6 months first or risk pregnancy complications, then an ovarian torsion that required treatment and recovery.
2nd pregnancy also ended in mc. It was a complex pregnancy and I had to have 2 surgeries as a result, during which the endo was discovered, I needed another surgery for that plus medication and other treatment. So that was another year waiting.
Then pregnancy 3 - dd - but medically far from plain sailing, bleeding, bad cramps, GD, spd, palpitations and fainting, preeclampsia ending in an induced birth 28 hours of labour and to save both our lives an emcs. Dd was very poorly and had to go into scbu. I too was very sick and needed treatment.
I was then advised another pregnancy would put me at high risk of death.
Out of my friends & family I'd say 1/3 have succeeded In becoming mothers without any issues with conception, pregnancy, birth or the child having a condition that is more likely to occur with older parents (sperm quality as the father ages is also an issue).
Quick tot up around 1/5 weren't able to become parents at all for a variety of reasons that don't include not wanting to be.
However this is a tricky situation with the personal relationships involved.
It's ultimately her and the potential fathers decision, but if her symptoms turn out to indicate an issue likely to impede conception, pregnancy and/or birth then the healthcare staff will point this out to her. That may well motivate her to consider ttc earlier.
Or...it's something easily treated and resolved and she'll have been checked over and found to be healthy enough to risk it.
But again even if that is the case, I'd be very surprised if none of the hcps say about the risks of late motherhood, and it's hardly a little known issue. There's lots in the news etc about it and her peers will likely be discussing too. It's highly unlikely she knows nobody that's had difficulties.
All you can do is listen, support and give your opinion/advice gently if asked.
My dd is 18. She has a disability which increases her risk of mc among other complications and possibly a gynae condition too. She's already decided that if she hasn't met the right person for her by the time she's 30 and she's financially stable, she's going to give serious consideration to going it alone rather than not be a mother. She will have my full support whatever she decides, though I will hopefully guide her in making sensible choices depending on how things pan out.
It's a difficult position you're in.
Someone I know the mum had multiple mc and then early menopause - which all the women in the family had - the daughter buried her head in the sand about all this, ended up unable to have children and at one point turned on the mother in her anger and grief and tried to say she hadn't been told about the family history, but she had. Took a long time for that relationship to get back on track.