Allen, 29 is set to perform with 21-year-old Cyrus during her US tour, reported Daily Star.
"She is incredible and she has such a presence. It's up there with an Oasis show or the Stone Roses or something. It is kind of incredible to watch - she is a real force," Allen said.
The singer is glad to be a support act again though.
"I am also excited to only play for half an hour. I am done by 7pm so I can go to dinner," she added.