Cresenta assumed the throne over Dirhhennia because she was an invalid.
Dirhhennia and Cresenta aren't necessarily Star's explicit great-grandmother/aunt, all of her grandmothers are referred to inconsistently in terms of their specific generational relation to her, aside from Eclipsa and Celena.
We've seen that Butterfly women who aren't part of the direct royal bloodline still have cheek marks, so it's likely Heinous is from a "black sheep" branch that's been separated/outcast for a long time. She doesn't even recognize Star as the crown princess, she's clearly out of touch.
I'd say it's telling that Star doesn't think she's a Butterfly, but Star doesn't even know who her own direct grandmother is, unless it's Soupina.