“Previous chaste character” is the sticking point. In fact, had it gone to trial, we might have a much better idea of who the biological father might be.
And remember, we don’t actually know that she was 17 rather than 18. We know she had Lauren at 18, that’s it. Lauren was born mid-December, so if her mother’s birthday was Jan-early April, then she was 18 at the time of conception.
This is not a good example of statutory rape. At best, it’s in a gray area.