Recommendation for anyone going to play the game, bring tissues.
@Raiper,
[spoiler=that fight]
There are different ways to end Toriel's fight and depending on how you interacted with other monsters you can change Flowery's dialogue at the end.
Also, get to critically low hp and let her attack you.
I'd say open up the spoiler after giving the fight one more go.
[spoiler=Different Ways]
Keep selecting spare until the battle ends
Keep selecting spare until she stops attacking for 3ish turns, then attack her.
There are quite a few secrets and endings to go for in the demo.
[spoiler=Ending Factors]
Kill/save Toriel then reload and do the fight again. Either killing her or sparing her.
The game remembers what you did on previous saves and Flowery addresses it directly.
[spoiler=Two secrets]
Go back into Toriel's house after killing her, listen.
Go back to where you fell at the start after sparing her.
Edit: I just realized how many spoiler tags I have and how good the demo is.