Check your love/intimacy points with the status screen. You need a score of 51 for her to survive. Notice that at this point in the game, talking does NOT affect intimacy, only headpats and events do.
Additionally, there is a hidden counter for trust points, of which you will need at least 5. You can only affect those through events:
- Molest her (-1)
- Give her a full meal (+1)
- Tell her you won't mistreat her (+1)
- Give her some chores to do (+1)
- Go out with her (+1) / Go out alone (-3)
- Buy her some pancakes (+1)
- Buy her clothes (+1) and tell her she looks cute (+1)
Finally, some choices (rape, smaller meal, no pancakes, not buying her the dress) automatically lock you into a bad ending.
TL;DR: less talk, more headpats.