A strong heroine doesn't have to be tough-as-nails down to the core. She can have a romantic side. One of my favorite kick-butt female protagonists is Rose Hathaway of Richelle Mead's Vampire Academy series. Rose is very urban-fantasy tough; she knows how to take down evil paranormal creatures.
Yet, her romance with Dimitri is so compelling and heart-wrenching. Typically, a girl who follows her boyfriend across continents and is still hung up on him after he tells her doesn't love her might seem kind of lame. But with Rose, you totally get her reasons and you know that she's right. She ends up saving Dimitri from a fate worse than death and she does a lot of crazy stuff to accomplish it. Even when the rational advice would be Get over him, chica.
Not that Dimitri is some boring guy. He's a strong, silent type, the kind of lone wolf you know you don't want to cross—which brings me to another point. Do strong heroines need an alpha male to keep things interesting? Or does a male romantic interest who takes the sidelines so that the heroine can really shine also work? I know the idea of a guy on the sidelines doesn't exactly seem drool-worthy, but does he have to be?
My friend and fellow author Janine Southard and I were recently discussing Nancy Drew's sidelined boyfriend Ned. As a teen, I thought he was beyond boring and I wondered why Nancy didn't get a bf who would go on adventures and solve mysteries with her. But Janine pointed out that there is something nice about a guy who lets the girl take the spotlight. And when you think about it, literature is absolutely overflowing with male heroes with rather forgettable female romantic interests. Those stories aren't about the romance per se, even if getting the girl is part of the goal. They're about the hero's journey. So why not do the same thing with female protagonists?