If shes old,overweight and likes to go slow ----poledancing is the go.
Yeah, you should know by now Im just stirring.
Let her do which ever makes her happy and lets you get on the water the most.
If you get her into either sport that requires wind,
she wont try and make you go for a pick nick in the country when its blowen 30knots, instead she will be dragging you down the beach.
But if she is inflatable as KOTP said,
Dont take her outside in 30 knot winds, if you lose your grip on her you may never see her again.
be happy she is interested in a wind related sport, there is alf your battle won right there.
makes decisions so much easier, plus holidays will always be somewhere windy.
another good reason to let her kite: if/when you split, she gets to keep the kite and you the windsurfing equipment. again, what more can you possibly want??
of course if you're married, she might get the house too, but that's another debate...
Who is going to do the dishes scrub the floors and feed your dog When your out on the water.
My eight year old son wants to kitesurf. I'm looking at military boarding schools at the moment . 
You guys are funny!