I think you're doing a marvelous thing and she will have a blast! And no one could say anything to you as I think hope you are doing what 99% of us should do:

they are not of legal age to drink - it just seems ludicrous anyone would be unhappy with you.

Sit back and enjoy -- I can't wait to hear what a marvelous time they have!

And so sorry about your daughter not being invited...I know all too well how painful it is. Much love to both of you!