what makes ladies clubs ladies clubs?

Typically its shaft flex but often they have weaker lofts to accomodate a woman's slower swing speed.

Isn't shaft lengths different as well?

That I dont know.  I would imagine its the case though.

Bad idea. Find a used women's set - or a new set - at a golf shop. Let her hit the clubs to see if they fit her.

blaylock , get her a lesson or two so she knows what to do. It's a bit late in the year for golf clinics, but individual lessons might help.

Some details on women's clubs: In the early 2000s, the golf OEMs started doing golf club design specifically for women. Some women who are taller and/or have a softball background can play with R-flex clubs. But, they are in a minority.

The average woman needs help getting the ball airborne. More flexible shafts help. Also, women tend to have less clubhead speed, giving them less distance separation between irons. So, some sets run 7, 9, SW, and skip the in between irons. See WSJ article by Timothy J. Carroll for more info: http://online.wsj.com/article/SB121372702050581575.html

And as women's clothing has petite lines, so do women's clubs. The petites are for women 5-foot-2 and under, and have shafts an inch shorter than standard women's; lie angles are also flatter. A site for women's petite clubs: http://www.livestrong.com/article/376194-the-best-womens-petite-golf-clubs/

All of the above is good advice, flex, length, loft, but what I think is the most important part is swing weight. Men's SW is typically D-0 and down, most men's clubs are D-4. Women's clubs are typically C-8 and up. Taking a inch off a D-4 could bring the SW down to about a D-1 or so but the static weight will still feel heavy. To me, lighter heads, shafts and grips are the way to go for most petite women.

If she takes couple's lessons with you, the pro can get an idea of what flex she needs in the early going.

Whatever, don't just buy a set and hope it works. Let her test it out first. Also, find a golf shop that carries L-handed women's clubs.