That’d be frightening, I don’t think getting eaten is something to take lightly, that’s something she wouldn’t get used to or don’t take seriously.
I’ve thought about a variant of what you say. In my fantasy, I set up a number of days and tell her for example "Sadly for you, I will eat you in 45 days, that’s not negotiable, I’m just being upfront with you so we can enjoy our time together until you become a small meal for me*. The don’t mention it again, maybe some small suggestion like “It’s sad this fun is coming to an end…” I’d be curious about how much she mentions it, tries to bargain or take account of the days.
Would she know how many days she has left? Would she become insane the day before she will get eaten? If I really plan to do it this sort of stuff can spice things up.