You do need to have a minimum Mind value, but it’s so low you’ll have it because there aren’t really those powerful Mind-punishing moves available before the branching point. It’s 40 for Esperia but hers shouldn’t be anywhere near that at the branching point.
Esperia has the second highest priority level (after Aselia) so you’re definitely getting Uruka instead because you’re not getting Esperia to a baseline favourability and mind (40 each) There’s no specific necessary choices.
I don’t know what guide you’re using; I used http://www.remus.dti.ne.jp/~jun31974/jkweb/capture/aselia/index.html when I first played the game yeaaars ago.
The branching point is the 10th turn of that long waiting period in Chapter 3 and the heroine whose scene you get is the one you’re locked into. I guess just make sure you didn’t totally damage her Mind value somehow before then. No way to check favourability, unfortunately, but if you picked choices relating to her in the fortune telling at the start (2, 1, 2), kept her in Yuuto’s party and picked obvious choices that favour her you should be on the right track. Her route is not a difficult route to get into.
EDIT: Whoa, I missed this:
Killing spirits is detrimental to Mind. Make sure you’re not overdoing it! Killing everyone with the same characters sounds like a good way to overdo it. Keep Esperia’s Mind over 40- that much is essential. I suspect her favourability is fine but you’re devastating her Mind with that strategy.