I'm not sure what that means, but I think a more appropriate term would be heroic couple. I think super couple is something they use for soap opera couples who move the story forward through their relationship: like Bo and Hope on Days of Our Lives or Zack and Kendle on All My Children. Yes, I know who those people are. Shut up, now you know who they are, too.
In contrast, I think a heroic couple is just that: two heroes paired together romantically. So, Holmes and Watson wouldn't count (unless you really read into their stories) but Han Solo and Princess Leia would, because she really likes that he's a scoundrel and he really likes that she's hot and rich. Other examples include Johnathan and Mina Harker from Dracula; or John and Maureen Robinson from Lost in Space. But, super couple and heroic couple are relative terms, and I have often heard them used interchangeably so if you prefer to refer to Meg and Garrett as a super couple, I won't stop you. However, a super-couple doesn't have to be heroic: the fictionalization Bonnie and Clyde, for example, or Megatron and Starscream, who--and I don't care what anyone says--were totally a couple.
Meg isn't as much a hero in the first book as she is someone who seems to stumble into one great situation after another until something bad happens. She doesn't decide to take an active role in her fate until near the end of the book, which is actually a big turning point for her and the focus of much of her narrative. Garrett goes through something much like this as well. By the second book, the couple is making things happen together. So, I'd say that they manage to become a heroic couple by the end of the first book and into the second, but for most of the first they are just getting things hammered out. I don't necessarily mean "hammered" in a sexual sense, but there is quite a bit of that. The events surrounding their lives grow apparent in the second book, and their role in it together is solidified by the third.