You have given this a lot of thought! Your friend should be ready to sign up for lessons any minute

I like dancing mostly I think because of the way it feels to be in tune with my self, my partner and the music. There are times, even in a crowded group class when everything is right and the room disappears and we're dancing on a cloud - the moments of "flow" or "the zone" or whatever you want to call it. It doesn't even have to be great music - we love to waltz to schmaltzy old Englebert singing the Last Waltz!
I think you could really emphasise the fun part. I have noticed that in our beginner's classes everyone seems to have a great time, even those "two left feet" couples. The mistakes are sometimes as fun as the great moments. DH and I have laughed so hard at our own goofs we have practically brought the class to a standstill a couple of times - let's just say that as Latin dancers we make pretty good waltzers...
I love the clothes, too. I am not a clothes person really. I just tend to wear what fits and is comfy. But special clothes for special functions - that is a whole other story. I still have boxes of crinolines and custom made matching outfits that I sewed for square dancing nearly 30 years ago and I am excited to be shopping forand sewing new ballroom clothes, at least as much as the budget allows. Don't get me started on shoes! If she is a shoe gal, she'll love some of the fabulous dance shoes.
Also, dancing inspires my imagination. I can sometimes see myself in hoop skirts a la Scarlett O'Hara, floating around a ballroom in Atlanta or Rhumba-ing in some smokey Latin disco in something with twenty pounds of sequins on it and not much else. I still see jive in proper 50's attire, though. Seeing the pros in competition in their Latin gear grates on me a bit

I love to dance because it is one of the things that brought DH and I together and because it is one of a very few things we have in common. We are a bit of an odd couple and we have had to work hard at finding things we can enjoy together over the years. Dancing fills that need and gives us something we can do together as long as we are both still standing and breathing. Oh, and I LOVE the looks of envy other women give me when they hear about us dancing. If men had even the slightest idea of how much women go crazy over a man who can dance, they would all be lined up for lessons tomorrow.
And remember that we are just beginners! I am sure that in a year or two my list will be longer. I honestly can't see much of a downside to dancing, especially for someone newly single.