Wayne beat me to it - again!
Even with a four-hour layover, I don't think I'd want to leave the secure area. Hobby just got scanners, and from what I've read online, they've really slowed down the screening process, going from eight to four lanes. That's just anecdotal info, though. I've not seen it first hand.
I haven't flown out of Hobby since January, and I always fly out early in the morning, but even early in the morning, security took awhile. (Of course, back in January, all the tu-ers were going to some football game that they lost, so it was extra crowded. Hope they don't do that again this year! Oh, wait! They're all playing golf this year instead.

)
Also, there's not any easy way to get to and from Hobby, except by cab.
The Houston Airport System is pretty tolerant of airplane spotters and photographers. We have a group here (
HoustonSpotters.net), and we have developed a great relationship with HAS. If she is a photographer, particularly an aviation photographer, she might be able to get some neat photos. I've never done any inside the terminal, so I don't know the protocol. If you'd like, I'll check with the Houston Spotters honchos tomorrow, and I'll be able to report back tomorrow night.
Otherwise, she can just while away the time with a good book and a fairly good meal (there are a couple of decent restaurants there).
Yes, the 1940 ATM is close by. That's where I'd go, if I were going to leave security. It's closed on Mondays, though:
The 1940 Air Terminal Museum - 713-454-1940
Let me know if you want more info.
What day is she going to be here?