Just pick a standard green snap bean, like Blue Lake (bush), Provider, Derby, Contender, Greensleeves, Green Crop, Valentino, Burpeee's Stringless ..... Unless you know what you want leave the filets, Romanos and others till later. These will be consistent with the green market types and very easy to grow. The purples are just as easy to grow, used the same way, but it might take her by surprise in their appearance.
Burpee or Ferry Morse seedracks found in most garden centers will have most of these.

Here is a link that might be useful: Burpee Beans.

The only thing I would add is to try growing a bean that tastes better than the ones she gets in the store. Several varieties are available that would fit including most of what Farmerdilla suggested. For an early Blue Lake type, Venture is excellent. Festina is another that has excellent overall traits of production, flavor, and appearance. Both are available from Park Seed Co.

Park Seed Co

DarJones

This year, I really liked Empress(Bush), which is a snap bean.

You might consider growing a few wax/yellow beans and I liked the Cherokee Wax(bush) this season.

Good Luck!

Dean

Thanks for all your input! I've heard ones like Blue Lake and Kentucky Wonder advocated heavily in other threads. Which of my factors don't they fulfill?

1. Unless the bush form is specified, Blue Lake and Kentucky Wonder are pole beans. 2. Definitely not supermarket types. Of the bush forms, the several cultivars named Blue Lake are comparable to supermarket beans. The several cultivars of bush Kentucky Wonder have been major dissapointments for me. Any similarity to the real Kentucky Wonder is very hard to find nor have they been top drawer fresh market green beans.
If you are stepping up to pole beans both Blue Lake and Kentucky Wonder are good. Blue Lake is much more stringless. My wife hates string beans, I grow a few pole beans because I love the flavor, but I have to eat them by myself.

Pole beans are not supermarket types mainly because they produce over a longer period than bush types and they need something to climb, which makes them poorly suited to mass production. But Blue Lake and KY Wonder pole beans are a fine place to start for the home gardener who wants to have a supply of fresh snap beans over a long period.

My recommendation for a "starter" bush bean would be "Greencrop". Excellent flavor, fairly large pods, and a very good yield. They do need to be picked young, though.

For a pole variety, "Fortex" or "Emerite". "Fortex" has 11" pods of excellent flavor, and is disease resistant. "Emerite" has more manageable vines, and round, very straight pods which stay very firm when cooked or canned. Both varieties stay stringless for a long period, so you don't have to pick them every day.

Oh, another factor I failed to mention. The spot I have picked out gets about 8 hours of sun. That's enough for tomatoes, but is it enough for these bean varieties?

Contender(1950 introduction), Cherokee Wax(1947 introduction) and Top Crop(1958 introduction) are very good producers of flavorful tender bush type beans you can get seed easily for. These are older bush varieties. Newer types tend to be more tough with a lot of fiber since they are bred for mechanical picking/harvesting. Old varieties are more tender. The above listed bush green beans are very fleshy with a delayed bean development but you can let them fill out for a more old fashioned type.

Blueflint

Eight hours is great! I grow beans in two different locations that get about 6 hours of direct sun but both have a big open shade the rest of the day. I'm sure they would do better with a little more sun.
I agree with all the others above on varieties. Fortex is the best flavored and most prolific pole bean I've grown and Roma II is the best and most prolific bush bean but it is flat and wide not like most supermarket beans.