First of all, good luck and all the best to your proposal!

And also, there's no harm in a bucket/box of flowers - preferably something medium (not too large) that she can carry with.

Just curious, do you know what kinds of flowers that she likes? The reason I'm asking is because 1 of my friends proposed his gf few years ago, and he legit proposed her with a box of ferrero rocher Was really nice and they were able to immediately sit and eat right after that surprise, quite neat actually.

Do you have an inkling on what item she might like?

Personally, if you ask me, I'd say you could spend this achievement via bringing her over to a fine dining, somewhere fancy. You mentioned that she's already have lots of items (bracelet, necklaces & stuffs), so I don't think it would hurt to try something different like this.

Or, buy a jigsaw puzzle for her. The one that has like 1k pieces of puzzles in it. That way, you could spend some time with her on puzzling, plus, it's not too expensive and/or 'glamorous'.