Good prospect vs. journeyman/gatekeeper bout. Slight step up in competition for Casey against a woman who is a frankly unremarkable talent at Flyweight (especially compared to her sister), but is at least well-rounded and experienced enough that she's guaranteed to be able to either:
A.) Expose O'Neill as an overrated can-crusher who got fed a bunch handpicked fighters of questionable quality in a promotion run by her own father following a hit-and-miss amateur career.
B.) Show that she's actually pretty legit and has grown over the course of her career with each fight -- something she has shown glimpses of (getting finished in her first two ammy fights before going on a finishing streak, going pro, leaving Daddy's Eternal MMA promotion to fight legitimate competition in UAE Warriors and earning a finish before finally being signed by the UFC, etc.)
I would not be surprised by either outcome, but at this point I'm siding with O'Neill. I feel like she has a bit of upside to her and has improved a bit as she's come along. Enough to at least get over this hump.