I'm originally from La., but have lived in Dallas for about 27 years.
Dallas is not a huge real cowboy town. It's more like an "urban cowboy" town, if you saw that movie. There's more big blonde hair and guys in suits here than there are guys/gals in cowboy hats. (The financial industry is big here.)
Houston is more a real cowboy town AND an urban cowboy town.
Speaking of cowboys:
FOOTBALL is HUGE here, this being the home of the Dallas Cowboys. There's a new stadium in nearby Arlington (a suburb).
Dallas is home to the Texas Rangers baseball team. They made it to the playoffs last year. So she could go to a home game, if she's here during that time. (I think we have a hockey team, too, but I'm not sure. And there's the Mavericks basketball.)
MONEY: Dallas is a pretty reasonably priced place to live. I think your friend may even be shocked at the good cost of living here, compared with Japan and other large cities.
SIX FLAGS OVER TEXAS: Larger than Disneyland/Disneyworld (whatever), and loads of fun. Rides of any and all sorts, food out the wazoo, acting skits, you name it. It's in nearby Arlington. Very easy to get to.
The Dallas economy is diverse: Banking, headquarters of companies, the apparel industry, oil & gas. Mainly because of tax advantages and DFW, a large, well-planned airport that is one of the main airports in the country.
Public transportation: Dallas is very spread out, compared to its population, so using the minimal public transportation we have is a problem. We have a bus sytem and a rail system. No subways. It's difficult to live in Dallas and get around w/o driving. There are wide expanses to cover w/no reasonable public transportation. It CAN be done, if you hitch rides with friends and plan carefully (choosing a place to live near the rail, etc.). I couldn't do it.
To give you an idea, Dallas has about half the population of Houston, but has about twice the geographical area. Your friend from Japan will probably find Dallas sparsely populated, compared to Japan. I can walk down the downtown streets, where I work, and not brush shoulders with anyone.
Golf - I don't golf, but Dallas is HUGE on golf, so there should be no shortage of places for her to golf, either public or private clubs. The private ones will be costly, I guess.
Restaurants - Dallas has tons of fine restaurants. Every kind of food imaginable. I don't enjoy eating out, so I wouldn't be the one to recommend specific places. If your friend is interested in Japanese, though, I have a friend who loves food and everything Japanese; she would be able to recommend excellent Japanese restaurants in the area.
Things to do and see: Dallas has on the outskirts places where you can take horse riding lessons, or rent horses to ride, if she already knows how to ride.
SouthFork Ranch: I guess your friend may not be old enough to remember the TV show Dallas, but it was filmed at Southfork Ranch, which is not too far north outside the Dallas city limits. Interesting...and amazing (disappointing?) at how small it is, compared with how it looked on TV.
State Fair and Big Tex: Have her see the movie, "State Fair" (any one of several remakes - my favorite is with Pat Boone), and then go to real State Fair. It's the same one. It's still here. This is one thing the bus system does well...it runs frequent buses to the Fair from various areas, and drops you off in front. It's very easy.
Dallas Summer Musicals: At Fair Park. Easy to get to. Easy to park (also, the Dallas bus system runs buses to Fair Park). Good musicals. (Fort Worth has great musicals, too...at Bass Hall. It's small, easy to get to, good acoustics, easy to park.)
Dallas has a good opera (I'm told) and symphony hall.
Museums: Dallas Museum of Art is interesting, but Fort Worth's Kimball Museum is better and has better exhibits (the King Tut exhibition went to Kimball, for example).
I hope she's not here from June through August. It's sizzling hot here, and the sun is super bright and glares. Dallas has a fairly high skin cancer rate, I think, so tell her to be sure and wear sun block during those months. And a hat. And very dark glasses.
Recommendations might be helped by accessing
http://www.zagat.com/dallas.Other things to see: Downtown has a World Aquarium. It's not big, but it's awesome. Plan to spend 2 to 3 hours there. As with other places, easy to get to, easy to park, the rail runs nearby, and buses go nearby. Driving is best in Dallas, tho.
The Dallas Zoo. It has a good reputation. I don't like zoos, so I've never been. But others tell me they had a good time. And a little train takes the people around; you don't have to walk everywhere, unless you want to.
Downtown Dallas: The Good Guys (tv show) shoots downtown occasionally, so if she gets lucky, can maybe see the two stars. I have. Near Thanksgiving Tower is where a lot of tv shows & movies are shot.
Shopping: Dallas is a great place to shop...you can either lay down serious money (remember, Ross Perot, former Prez Bush, Don Henley, and plenty of other extremely wealthy people live here), or there are tons of places to go bargain shopping. For anything. It's a clothing mecca, but anything can be found here. There is an Asian bargain shopping area, but I went there once, and it was hard to get around it (hard to explain), and it looked like just junk to me. I'll never go back, but others tell me I went to the wrong places.
Lakes: Dallas is land locked, but there are man made lakes around here. Some large enough for boating and whatnot. Others "inner city" with jogging/walking/cycling sidewalks. Needless to say, don't go alone at night. Dallas, like any big city, has a robust crime rate.
RODEO: Besides taking horse riding lessons, or renting horses to ride, there is the Mesquite Rodeo. Mesquite is a suburb, and that rodeo has been going on since forever. That is probably the one place she can see a collection of REAL cowboys.
The best thing about Dallas is, I guess, that it's a big city, but not too big. It's fairly easy to get around, so she shouldn't be afraid to drive here. Unlike Houston, the streets here were well planned, and traffic moves, with few bottlenecks (though they do exist). The people are fairly friendly. There are basically several major freeways that'll get you anywhere you need to go.
That's about it.