Changed dominance behavior

Question
My husband and I bought two guinea pigs about two months ago. I have checked and believe they are both girl piggies. For the first few months we believed the Popcorn was going to be the more dominant because of her actions around the cage and because Peanut was very submissive. Now, Peanut has come out of her shyness around Popcorn...today I noticed her rumblestrutting around the cage. This made me nervous bc I was afraid we may have been sold a male and not a female. I checked on how to sex them and she does not appear to have male parts. Is it possible for girls to switch roles in the couple? I have not seen any signs of them trying to "mate", but she is rumblestrutting around and Popcorn is now being the more submissive one. I'm slightly confused and wonder if this is normal. Could our guinea's have switched roles? Is it normal for a guinea that has barely made any noises (unless we were trying to pick her up) such as purring when we pet her or anything...to start rumblestrutting out of nowhere? Popcorn has always purred when we pet her...Peanut has never made a noise...now she rumblestruts. Sorry this is so long and hope I made since in what I was asking. Thanks for the future help or advice: )

Answer
yes its normal and so long as the other piggy isnt fighting for dominence then its fine, but make sure she is a female, while they do, do all of those things you never know she could be a he, if you know someone with a male then let them give you a look, you will see the difference instantly, most experienced guinea pig owners would know from the day the piggies are born which gender they are.