Dress buying help...

gogadgetgo

For my mom.  She's looking to get a new dress for a party celebrating the opening of a new mexican restaurant in her town.  She wants something fun and colorful. She wants my help finding something but I'm worried about finding something age appropriate (she tends to like stuff that's way to young for her).

Her stats:  She's 55, 5'8" and has a slender build.

 Any ideas?  Bonus for stuff you can try on in a store.  We have pretty much everything around us.

 TIA