PP don't beat yourself up. It sounds like she may not be ready yet. If you aren't giving it to her during the day then it's probably just how she's used to soothing herself to sleep. She's still only really little. My DD was 22 mths, so a fair bit older than your DD. We didn't need conversation, but she was old enough to self-settle in other ways obviously.

I doubt with your approach she'll be sucking her dummy when she's going to school!

(FWIW, I was never in favour of offering the dummy in the first place, figuring what was the point? But when my DD was only 2 days old she was frantically trying to suck her wrists after every bf and she wasn't hungry. The paed pointed out that she'd given herself blisters b4 she was born from soothing by sucking on her wrists - so out came the dummy and it was the best thing ever!! So I will wait and see with #2, but I don't think it was much hassle to get rid of it and it brought a lot of joy b4 then!).