[AnchorAlumna]

How about this: put the blame on your executive council.

"We'd love to invite you to our semi-formal bash but Exec won't let us. Please let us comply so that we won't get our charter pulled."
You can imply that it's just for a couple of years....which should be enough time to break them of the habit, and you can go to a format of inviting them to only certain things.
Your Exec (or whatever you call it) would probably be glad to take the blame! But discuss it with them or your regional officer first so that when those angry ladies call them to complain, they can back you up.

As far as a recent graduate (of the same chapter) serving as an advisor...sometimes there is simply no one else who can do it, but it's always preferable to wait to let her contemporaries graduate.