She lost all her expression magic when she in the S4 finale, now she's just straight up witch so if it was the expression magic that made her powerful enough to heal a vampire bite to the neck, then she should be able to at least take the pain away like she did with Elena. Unless, she could heal Elena and not herself kind of like how on Charmed, a white lighter can heal others but not themselves.
Bonnie kind of reminds me of Piper and Paige from Charmed, dies all the time but there's always a way to bring them back. She'll survive this
I don't know how she does it but she always does.