It's certainly a solid argument, though I remain hopeful it will turn out not to be the case. It feels like it's too similar to the Maya/Josy twist.
But since we have months to go before we can learn more, let's parse Bella's wording:
Bella does not put a gender limitation on the urge to touch herself, implying that has also been three years. And her response here is very different than when Jill tries to assure her 'it' won't happen again. In the MC's case, Bella decided to pleasure herself. In Jill's case, Bella knocked her wedding picture to the floor.
Granted, I may just be grasping at straws. But I think whatever the incident was, it was about more than making Bella inappropriately horny.