I can't agree that it is the only explanation. I see it as abandonment, and resentment that she won't be there only for herself anymore. To me, its the same feeling as when someone's best friend is getting married, and they are upset that they won't be able to spend the same amount of time...
Am I crazy for not seeing this as incest? She clearly states "No. Even if that were the case...". To me that reads as she's not romantically in love with her