Walsh told OK magazine that Harding's efforts to tackle problems with alcohol and depression had gone "really well".
"I'm proud she's facing her demons," Walsh said.
"It is brave as some people can't face up to things, and she obviously knew she had a problem and could help herself. I'm proud of her for doing it."
Walsh had previously said that Harding's friends were "all there for her" after she travelled abroad for treatment.
It was rumoured that Harding had been given a rehab ultimatum by her Girls Aloud colleagues to prove that she was serious about getting fit for their planned reunion tour in 2012.
Harding left rehab earlier this month and is said to be planning a US holiday with Cheryl Cole.
At the weekend, the singer was reported to have permanently split from her boyfriend and former fiancé Tom Crane.
Harding and Walsh were this week ranked 26th and 24th in Heat magazine's list of the richest under-30s in UK entertainment.
Watch Sarah Harding have a polo lesson for The Passions Of Girls Aloud below: