Most of these names apart from Mabel and Posie were fairly popular where I am in the UK when I was naming children 12ish years ago. Elodie, Darcy and Heidi were all on my list
Mabel - it's just the wrong side of old lady to me, but I can see it's sweet and why people like it.
Matilda - I really like it but it was fairly popular around 12 years ago. The couple of people I know personally with daughters called this call them Tilly
Polly - really really love, I think it's just lovely.
Posie - Not a fan really, it's a bit silly, it's a name for a bunch of flowers. I prefer Primrose which is vaguely similar.
Heidi - I loved the story when i was little and had a gorgeously illustrated book. i think it's lovely.
Darcy - Really like, it's a bit of a stronger name rather than a pretty name compared to your other options.
Elodie - This was top of my list 12 years ago, I thought it was really unusual before having my first child, but I think a lot of people thought the same as I believe there's a few Elodie's about now, or similar like Amelie and Emily.