you can do something fun and simple such as "Maria is getting married, come and celebrate with her before she becomes a married woman!" "Soon to be married..and celebrating! Join Maria for some fun!
A cute group party picture of the girls on invite it a good way to get people excited. You can also use a goofy picture of the couple or just a single goofy picture of the bride.
3D hearts, small bouquets of roses, or classy geometric designs would make for a cute invitation. Often times, colorful alcoholic beverages with 3D fruit, olives, or bubbles are nice.
Make the invitation in the shape of a diamond engagement ring. On the band, write "Let freedom ring..." On the inside add, "one last time for XYZ." Include party details.