She said: "It's slightly intimidating being in the band, of course, but it's huge. I was a fan before and want to prove myself. Everyone in the band has always been a strong vocalist and that's what I've been about."
Heidi also revealed Keisha is no longer speaking to her but is looking forward to the future with a new-look line-up.
She told Britain's Sunday Mirror newspaper: "Things came to a sudden end. We didn't think anything was going to continue at all. We were going to split - and we'd be over.
"Then management came to us and asked Amelle and me if we would like to carry on. And we did.
"The last time I saw Keisha was terrible. We didn't speak. I've sent her a message but she's not talking to me - she doesn't want to know. It's been years together with the band and it's really hard. Really hard. Everyone's nicknamed me Tiny Tears because I'm constantly bursting into tears."
"We've been given a second chance. We tried everything we could to make it work with Keisha but we couldn't keep it going with her. Life's too short to live in an unhappy situation.
"NOne Of Us were happy - her included. It was a difficult situation."