Here is an actual guide that I found
1. You can molest her, you just cannot penetrate her. There is a very telling choice that you can just come back from.
2. Story quest choices should have a slight bloodsplatter (do not choose them) on the death flag choices. For instance, when she first has dinner with you, there will be a slight bloodsplatter on the choice that isn't the one that gives her a proper meal. Once you learn to see this, the dialogue choices are easy enough.
3. As soon as you can take Sylvie outside with you, do so. Take the alternative path, buy her the clothes, then compliment her. The next day take her out, but take your usual route (appears at noon) and make sure you give her pancakes. These are the two interactions you need to do outside to keep her alive.
4. Inside the house, just use the loop button and keep headpatting her, and chatting her all day. You can go out and buy clothes for the first tick of day, I just like to headpat all day so I can get intimacy up for later.
Honestly, the first few days are just about rasing her trust and affection/friendship. So just be really nice to her, then at some point, she will ask you if you want sex.
Here are the photos for her getting sick
