Something I found that can help others to GET 4 HEARTS FAST!!!
Get some gems, doesnt matter which one, preferably the red one cuz u can craft them with tree saps. Or use cheat engine to get yourself hundreds of them. Have at least 20 of them in your inventory. Have another girl following u by choosing the 3rd option from bottom. Now just keep gifting gems to the girl you want to raise affection. For some reason, you can talk to the girl unlimited times when u have someone else following u. I don't know if this is a bug or feature.
Of course there is a long animation when a girl receives gifts from u. U can skip it by following your target girl until she is in resting animation (leaning against walls, sitting down, but not doing anything) You can keep gifting her gems without any animations. 20-30 gems later, you can ask your follower to get lost. And your target girl will be having red cool-down circle. After your target cools down. You can talk to her and trigger the special dialog to raise 1 heart. Talk to her 3 times and u won her hearts.
Keep in mind that I used cheat engine to raise my followers stats to thousands. Dont know if this is causing the unlimited interactions with target girl.
This method is basically trying to find a way to gift girls as much as I can in short time. Everytime u gift a girl, her affection grows. So gifting her gems to yield maximum affection, the follower thing is just to bypass the cool down.