Using "said" some of the time is fine (imho) but you can add to the mix some alternative expressions. For example, "... Meg asserted", "... Jen maintained", "...Meg insisted", "... Jen shouted" and so on and so on. However, I wouldn't get hung up on finding too many alternatives lest your prose become a bit clumsy and self-conscious! A bit of mixing and matching is needed perhaps?