So what exactly was the "Waking Up in Vegas" songstress doing in Sin City?
The pop singer was in town to help kick off 1 Oak nightclub's grand opening weekend celebration, cohosting its GiveLove Charity event at the Mirage hotel hot spot with her BFF, J. Molinari jewelry designer Markus Molinari.
"Happy to be supporting my best friend @MDMOLINARI & his j.molinari jewelry w/all my other besties in #VEGAS for a great cause @GiveLoveOrg," Perry tweeted Friday evening.
Before heading inside to the shindig, Perry presented a check to the charity's cofounders, Patricia Arquette and Rosetta Getty, and board member David Arquette (who was accompanied by girlfriend Christina McLarty).
The trio's charity develops temporary housing solutions and improved sanitation systems in Haiti.
And then it was time for the main event.
But, rather than party the night away once inside, the blue-haired starlet kept a low profile at her VIP table, where she sipped cocktails and hung out with friends for the night.
"Katy was pretty mellow," a source told E! News. "The group that she was with was partying, but she barely got up and pretty much remained in one place all night."
Perry went on to tweet about the evening, writing, "Thanks to everyone who helped out w/the @givelove event at Mirage & 1 Oak LV. Go to http://www.givelove.org to see how u can MAKE a difference!", Perry tweeted early Saturday morning.
–Reporting by Marc Malkin and Noelia Murphy