I don't think Keyes had anything to do with Jennifer Kesse. I won't rule out the possibility of course but I think statistically it's just too unlikely until we see some solid evidence that links him. Yes, Keyes very well could have killed dozens of people, but what are the odds that they'd happen to be the more publicized and/or mysterious disappearances in recent years (e.g. Kesse, Maura Murray, Brittanee Drexel, etc.)? Considering the sheer number of people that go missing, it seems improbable that these specific cases we're so invested in and desperate for answers would happen to connect to Keyes.
This isn't mean as a slight against the great sleuthing being done; just my personal opinion, as I am a firm realist and pragmatist (maybe to a fault).
EDIT: With all that said, though, Katelyn Markham might be worth looking into as a possible victim. Her case remains baffling, and a stranger abduction seems likely (as opposed to e.g. Jennifer Kesse, who I believe was probably taken by someone she knew well).
She disappeared from Fairfield, Ohio on August 13, 2011. Here are the closest of Keyes' whereabouts to that date:
June 2, 2011 to June 16, 2011: Midwest US, Eastern US
September 15, 2011 to September 25, 2011: Western US