If you have a miscarriage you don't normally dodge medical attention, fail to report it, and then bury the remains quietly in an unmarked grave.
https://www.vox.com/identities/2019/11/8/20954980/stillbirth...
In any case, such nuance is likely beyond the grasp of a 17 year old. I think you are well aware that this doesn't always yield simple seeming edge cases and that you are capable of looking into other examples but chose not to. Here's some more.
In this case it's a bit more suspicious, but it's not an unlikely explanation by itself.
They did. They found messages of the girl self aborting well into viability and then planning to hide the body.