That sounds really rough for her, I hope she finds more supportive people like you to counterbalance that.
I married at 18, had my honeymoon baby a month after turning 19, he's now a lovely teenager - couldn't be happier with him most of the time. I got a lot of shitty comments for a few years and I actually found people who knew I was married (particularly professionals, people in the baby group) were far nastier than random people who didn't know either way. A bit of immigrant hate was thrown in there to.
I teach my children that having a child under 20 is very risky in many ways. I took a major gamble, I knew part of it but not all of it when I rolled the dice. In most ways, it's come up great for me - great marriage, lovely kids, life younger me couldn't have dreamed of - but not so much when it came to my health - at that age, a lot is still being built up and if you tap into it so heavily with pregnancy, issues are more likely to happen. Some get away with it, some like me seem fine until the cracks show up later, and some pay the price right away. Lifetime disability is highest in under 20s as are maternal deaths, before getting into the social risks of isolation, the pressure a child puts on relationships, the higher risks to both mother and child if another partner comes on the scene (from studies I've seen, the idea of stepparents being more violent has mostly been debunked, but there is a higher risk if it's not really a consistent relationship - a fling which too many early studies condemning as proof of how bad stepparents are - or the stepparent is particularly young, under 25).
I teach my children that life requires balancing risks, responsibilities, and benefits. I have thought maybe things would have been better if I could magically shift them all a few years later, I would have been so much calmer in their younger years and maybe my health would be better, but then my younger children wouldn't remember their uncle or grandparents, so many other things would be different too. I accept the risk I've taken, but I want my children to know better before they consider taking them. I want them to have more options and know their options more than I did. I didn't, I fully admit young me mostly thought that seems better than where I've come from which it was and still 1000% is and took a chance that this couldn't be worse. I was right, but I know others that have been really, really wrong.
I teach them to respect others, and I also teach them - particularly my daughters - to push back against the idea that the proof of how worthy and loveable they are as a person is whether someone will fuck them or marry them. It's not true of all young mother, but way too many of us - including me - started young because we wanted to be loved, that love would fix something in us, and a relationship - intimate or parental - is evidence that someone loves us. The latter two aren't true and caring for a child makes figuring all that out harder. I wouldn't trade my kids and those experiences for anything, not even my youthful health back, but damn do I wish younger-me could have had people who taught and cared for me better, who gave me something other than that family image of adult happiness with those who said I'd never get it because of who I am. My children don't have that weight, but there are other social messages they get that cloud their options from time to time. I try to teach them to see beyond that as best they can, telling my teenagers who they are now is not who they're going to be in ten years and few know in their teens who they'll be later, but they're taking steps towards it one way or another.