The Olympic gold medallist - who has been seen crying on several occasions during her cycling career - burst into tears after last week's cha cha cha with partner Brendan Cole.
"It's frustrating because people only see the snapshots and think she is emotional," Gardner told The Mirror.
"But they'll soon see the real Vicky and how light-hearted she is. When it comes to putting in a performance, she is exceptionally hard on herself."
Pendleton made it through to the second round of the BBC competition after her improved Foxtrot performance on Saturday (October 13).
Gardner added: "When I see her starting to well up, I think, 'Come on, Vic, please don't cry again, it's not you', but she felt she had let herself down.
"Her poor feet are suffering. They are sore because for the last 10 years she's hardly walked anywhere. She was either on the bike or resting her muscles. Now it's eight hours a day dancing around the room in high heels."
Strictly Come Dancing continues with a Hollywood-themed show on Saturday, October 20 at 6.30pm on BBC One.
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