From Bulbapedia, the community-driven Pokémon encyclopedia.
Wendy (Japanese: ジンジー Gingie) is a character of the day and member of Team Rocket who appeared in Dues and Don'ts.
Wendy works in human resources for Team Rocket, and holds a grudge against Jessie because of something that happened years earlier. One day, they were working out together and afterwards got smoothies at the Rocket Café. Jessie left Wendy to pay for them and said "I'll pay you back someday." While Jessie forgot this over time, Wendy never did, and thus holds a constant grudge against her. Wendy got her "revenge" when she added the price of her smoothie to the trio's Team Rocket bill. Unbeknownst to her, Jessie didn't pay any attention to it (and even remarked that she didn't like fruit smoothies and instead preferred a mocha with whipped cream).
Wendy has direct contact to Giovanni and she refers to him as "master."