She is having a mermaid birthday party. Coral Reef for Aria's 5th birthday.
It is made from pool noodles, coat hangers, floral mesh, brown kraft paper and tissue paper.

reference :
http://www.craftymorning.com/pool-noodle-coral-reef-craft/
http://www.teediddlydee.com/diy-pool-noodle-coral-reef/
http://www.pressprintparty.com/diy/party-decorations/make-coral-reef-decoration-sea-party/