A.L.
I 'm not creative, however I'll take a stab at answering because I'll be in your shoes sooner than I can imagine.
I vote for balloons tied to a gift weight--how about weighing the balloons down with some chocolate kisses wrapped in a piece of foil, like you described? You could have a separate balloon and weight for each guest. Perhaps your daughter can get together with some of her pals, cousins, etc and make the weights, so you don't have to spend the time? They would have a ball, I bet. And she can rehearse some of the prayers together with them, while they're at it :)
As for your daughter's feeling that they aren't 'enough,' my first thought was 'Shouldn't she be worrying about her Torah portion and commentary rather than this?', but I understand she's feeling pulled between wanting to have a fancy event and knowing there are limits. She may need a reminder that you're on a budget and you've already spent X dollars for the meal, location, DJ, her outfit, etc. Has she seen a spread sheet with the costs? It could be a good reality check for her.
Mazal Tov in advance, and I hope the day is lovely!