Whenever I talk to her, she just says "keep walking broke boy" and says something about how maybe she'll come after me when i lose or something. But given that I've been playing this game for a while and am now at level 28 or so, I don't think anything in the forest will actually be able to beat me, so deliberately losing isn't really an option. Am I missing something?

That’s Megan you’re talking about—you do need to lose in order to get her reward. If you’re a high level, you can still lose by upgrading your magic defense at Vanilla’s shop, which deals a small amount of damage. Additionally, there are higher-level enemies in Ivy’s dungeon that can wear you down.

Eva is also found in Ivy’s dungeon as part of the main quest.