Piper bowed out of the popular BBC One show in 2006, after playing the Time Lord's assistant for two full series.
She will be seen in the 21 June episode of the current series - her first full appearance since the Doctor left her in a parallel world.
"I wouldn't have missed this for anything," the 25-year-old told Doctor Who Magazine.
"It means so much to me, this show, and so do the people that make it, so I really wanted to be here for these final episodes."
Piper admitted she had to do a little homework before slipping back into the role.
"I had to watch a lot of the old stuff, so I could remember certain things about the character, because I've been playing posh birds since I left Doctor Who," she said.
"Rose is a bit of a chav, bless her. I needed to hear the voice and watch the posture and everything, but then the minute you get on set, and you've got Russell T Davies' scripts, and he remembers how to write so well for Rose, you're back there on day one, really."
But Piper, who recently married actor Laurence Fox, promised a few changes for her character.
"She has changed. She's hardened. She's been through a lot in her parallel world. I think she's been through emotional turmoil.
"She's quite sad and lonely, but also really bolshy and - that great quality that Rose has - just so headstrong and single-minded."
Despite her guest appearance, Piper maintains that leaving at the end of the second series was the right thing to do.
"I did feel it was time to leave, but not because I was bored, just because on a professional level - and on a personal level, actually - I felt that I needed to take on a different challenge," she said.