The police exhumed the body because the 22-year old man who helped bury the body made a police report. The police didn't seek the Facebook search warrant until after they exhumed the body and found evidence the body was burned.
Given she is underage and pregnant, who made her pregnant? Why are they so desperate to conceal the evidence of the miscarriage, to the point where they burned the body, was it to prevent DNA testing?
That's just the tip of the iceberg here. It needs to be understood why they took this course of action.
A teenager getting pregnant from another teenager is extremely common, and likely more common than the alternative. Burning a body is also an extremely traditional, something like 60% of Americans are cremated. Suggesting the police need to be involved in totally ordinary circumstances seems silly to me.
You do if you reasonably fear you're going to be criminalized for seeking medical attention. Here's an example from a few years ago (so reporting is not shaped by current events), and you can find many more recent examples.
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.