so, there are two different kinds of routes in this game - full routes and secret routes (with some weird ambiguous edge cases like jarrod and lisle). the full routes are generally with the kinds of people the matchmaker would approve of you pairing off with, and they get week three dates. gisette is a secret route, so she doesn't get one. if your relationship values are high enough when you're going to see the matchmaker for the last time at the end of week three, she'll interrupt you on your way there, send jasper away, and imply that she's interested in you. (if you go to the gazebo right after the horse incident in week two you'll have a scene with her there that comes with a relationship boost, a stat boost and a CG, which are necessary to get the values high enough, i think?)
i'd actually avoid pursuing jarrod if you're interested in gisette unless you have the stats to talk him down after rejecting him - just be evil and avoid him, and gisette will do the rest
also, your relationships with Everyone are reliant on how well you perform at events, including the self-hosted ones - everyone you invite gets a big boost of friendship, respect, and potentially romance, which is great for building romance with the secret routes!