SO!
Let's actually run down the stuff here, as well as some ideas that aren't actually in the planning doc.
Some people seem kinda confused at the whole points and tallies thing. To sum it up: She gains or loses points based on the outcome of combat. She gains 1 point for winning, 1 point for winning without any of her party going down, and vice versa for losing points.
-5 and 5 are points where she turns into her intermediate forms. These forms have slightly altered stats and moves. I figure she'll stay in those forms until she either goes back to 0 or to 10/-10
-10 and 10 are the points where she turns into basically a mini-boss. Her stats are higher, she's a higher level, but her encounter rate becomes much lower. She will stop gaining or losing points when she reaches these forms (onto the things that aren't in the doc right now). To get her back to normal, a new encounter will appear. Basically it'll be her handler; a demon, or demon-morph responsible for not only keeping her under control, but also channeling energy into her to cause her to change in the first place. If you beat him, he'll lose his channeling and she'll go back to normal, resetting the whole thing.
You won't be able to do anything about her on the initial encounters in The Frostwood. When you get to the Windy Peaks and start encountering her, the channeler will be a much harder fight, but at the end you'll have the option of either destroying his control staff to free and purify Eisheth, or take it for yourself and have her as a pet. In either case she'll become a follower.
Now, tallies work on basically a strike system. If you have three tallies, you get a bad end if you lose to her again. Tallies are only gained against her 10/-10 forms, and are removed when she is reverted. Tallies come with TFs, the TFs are set, so they're the same each time. They don't go away when the tallies are removed, but you can get them removed by a healer, in case you want to keep them. They probably won't stack, meaning if you don't get them cured, adding more tallies won't add more TFs, so you can't use them to cheese TF yourself.