Giggles and Petunia are two of only four females on the show. Both seem to be best friends in many moments during the series, and also do a lot of things together, such as having a tea party or lunch together.
Giggles is seen to be best friends with Petunia in many occasions. They are shown doing things together like having a tea party in Stayin' Alive, co-owning a lemonade stand in both Eyes Cold Lemonade and Gems the Breaks, trick-or-treating together in Remains to be Seen, admiring Pop and Cub’s Christmas lights in Stealing the Spotlight, sitting on a log together in Ski Ya, Wouldn't Wanna Be Ya!, cosplaying together in Wrath of Con, playing poker together with Lammy and Flaky in Royal Flush, dancing and relaxing on the beach in Put Your Back Into It, riding a roller-coaster in The Wrong Side of the Tracks, eating breakfast and working out in Ipso Fatso, flirting with Mime in Easy Comb, Easy Go, and dancing and wooing over Lumpy as well as kissing Cro-Marmot in Wipe Out!. In Happy Trails Pt. 2: Jumping the Shark, she is shown mourning the graves of multiple characters, including Petunia. She also immediately tries to help Petunia when she catches fire in Who's to Flame?.
The only mark against her opinion of Petunia is in Wrath of Con, when she accidentally cuts Petunia in half with her lightsaber. She shows very little, if any, concern for her friend’s death, only confusion about how it happened.
Likewise, Petunia is obviously Giggles' best friend as well, and she voluntarily and happily goes on all the previously mentioned activities. She even invites Giggles (as well as Mime) over to her house to have breakfast in Who's to Flame?. She is also one of the friends that volunteer to help build Giggles a brand new house in Home Is Where the Hurt Is, and is the one to cover her eyes for the surprise. She is also horrified by Giggles’ injury/death in Stayin' Alive.
The relationship is not perfect on Petunia's side, however. In Eyes Cold Lemonade, when Giggles’ face is ripped off by the sign, though Petunia is shocked, she spits lemonade onto Giggles’ raw flesh, only worsening her injuries. Furthermore, once Giggles is wrapped up, she seems to have become completely apathetic. She also completely disrespects Giggles and Mime as her guests in Who's to Flame? by taking a phone call without asking, and seemed ready to engage in a long conversation with the person on the line had she not caught fire. Instead, common curtsey says she should have let it ring or told them something like “I have company over, I’ll call you back.” It could be argued that Petunia likes Giggles less than Giggles does Petunia.