Or find ways of splitting up the party, a good example of creating time sensitive requirements in an adventure would be Dead in the Water, if one of the players really wants the combat monster encounter experience more than roleplay, design encounters for that and find ways to make her group experience that more often, and set aside other encounters for the other players, it may be that watching the others roleplay will make her more comfortable with the premise.

Plus the combat encounters can be made more challenging without the fear of wiping out the rest of your players at times.

I'd recommend checking out Robin's Laws of Good Gamemastering: http://www.sjgames.com/robinslaws/

It breaks down player into a few specific types and gives advice on how to develop games that appeal to each type, including the "Casual Gamer"--often somebody's roommate or boyfriend who's just along for the ride but not too invested.

If you know "I've got two Butt-Kickers, a Storyteller and a Casual Gamer", then it helps to make up scenarios. "OK, we'll need a good fight scene for the Butt-Kickers and maybe a dramatic betrayal for the Storyteller. Maybe give the Casual Gamer's character something specific but not too complicated, like sneaking around during the fight and slicing a terminal."

I'd echo everyone else's suggestions to experiment with a really simple story that might take only a single session to resolve. Depending on the length of your sessions, this could mean one fight scene and one dramatic scene, or it could mean a bit more.

The suggestion of taking an "A-Team" style story is great, because they can be very simple and you can resolve it all in one session.