Obviously Madeline Duggan worked closely with Tom Law, and Jacqueline Jossa worked closely with Ben Hardy.

From what I can recall, Jacqueline Jossa took over the role of Lauren before Tom Law left Eastenders.

Did New-Lauren work with Old-Peter at all?
Just really curious, as I genuinely can't remember

Yes, there was one scene where they'd been drinking in the park but Peter wanted to go home. Lauren was trying to encourage him not to when Carol saw them and went ballistic. This was just after Billie's alcohol-related death.

Yeah Old Peter left in December 2010 and Lauren return in September 2010

That was around the time I started watching EE and got seriously confused when Lauren's head changed out of the blue. But the thing is the actor's looked so alike it worked.

Lauren was one of the most successful soap recasts ever IMO