Suffice to say the similarities between her and Evergreen are striking, the only major difference being that Evergreen is pretty obviously a straight up villain, where as Flemeth’s nature is a bit more ambiguous.
Evergreen: Helps you out on first meeting, gives you quests, gives you transformations, many of them for the price of just some smooching, helps you build your Wayfort if you ask, and generally is content to hang around and add to the Tanuki population, making vastly more daughters than she'd ever need for body-swapping purposes even if it was true never really challenges you or threaten you in any way, and rather warns you against Kasyrra and the power of Lethicite - clearly a straight up villain!
Flemeth; Saves your life for her own purposes only, sends you off with one of those daughters ready to lay the groundwork for Flemeth's intents to get the powers of an Old God that predates even her, intends to kill said daughter who is your primary love interest and means of surviving the game without letting someone else die for you, and you probably end up fighting her in some capacity in all three games, and even "kill" her in the process, hints she may be one of the most ancient slave-masters of the world just wishing to get her old strengths back - I mean that's clearly a bit ambiguous, could go either way right, let's give her a chance!