Before the Gym battle, Roxie is seen in Virbank City outside of the Pokémon Center, arguing with her father about him becoming a movie star. He defends his wishes by commenting that Roxie balances her duties as the Virbank Gym Leader, and as a member of her rock band. He leaves, and Roxie gets angry and heads for the Gym, which the player can directly challenge.
After the Gym battle, Roxie can be seen near the port with Hugh and several of the Team Plasma Grunts. After the battle that follows, she gives the player the HM Cut and then heads back to the Gym.
Roxie later makes a brief appearance after the player competes in the PWT for the first time, expressing an interest in competing in it (causing Clay to remark that word of the competition is spreading). Roxie does indeed compete in it later, along with most other Gym Leaders.
"Get real! You're a captain already, aren't you? If that ship doesn't move, you're going to cause lots of trouble!"
"AAAAAAH! You dim-witted...dense...dumb...daft...dippy...dorky...doltish DOFUS! Doing double duty isn't the problem! You're causing problems for people! Keeping people from getting where they're going because of sheer selfishness is unforgivable! I've HAD it! I'm going to the Gym!"
"Hey! You two! Haven't you got any wild and crazy Pokémon battles to show me?! Guess I'll have to enter the tournament myself and rock the audience right outta their seats!"
Before battle (first round)
"Get ready! I'm gonna knock some sense outta ya!"
Before battle (second round)
"Fight with this Pokémon that way... Use this item that way... Are you letting others decide that for you? Well, whatever, but what's important is figuring out what you want to do! Get ready! 'Cause I'm going to knock the common sense outta you and drag you into a brand new world!"
Before battle (last round)
"You don't do anything! What do you know?! You don't do anything! How're you gonna change?! But, I've got you covered! I'm gonna give your reason a toxic shock and open up your mind!"
"Wild! Your reason's already more toxic than mine!"
After being defeated
"You didn't win... I lost! I was weak and made my Pokémon feel how much losing stinks! Watch out! Next time we meet, I'm going to give you a toxic shock!"
It's kindness to say no for your friends and Pokémon, right?
Jingle: "Woo hoo! All right! It's 'The National Gymquirer'!"
Page: "That's right! We collect the hottest gossip about Gym Leaders seen around town! Here is today's letter. From someone going by the name RoxieForever! Thank yooou! 'This is a story about the first time I ever went to one of Roxie's shows! Many fans collapsed from the toxic power of her songs. Roxie's really a toxic shock to the system, isn't she?!' Maybe they were just too excited and fainted. Make sure to drink lots of fluids when you go to concerts! 'The National Gymquirer'! We eagerly await your letters!"
Roxie proved herself to be a very capable Gym Leader, defeating five of Ash's six Pokémon despite being at a disadvantage in terms of her party. She would occasionally perform a riff on her bass during the battle, and the crowd would chant her name. When she was defeated she happily congratulated Ash as the crowd cheered for his victory, and she presented him with his eighth and final Unova Badge, the Toxic Badge.
This listing is of Roxie's known Pokémon in the anime:
Koffing was the first Pokémon Roxie used against Ash in their Gym battle. She captured it while she was in Kanto, and it inspired her to assemble her rock band, "Koffing and the Toxics." During the match, it defeated Ash's Boldore and Unfezant rather easily, but was later defeated by Leavanny.