...how could I refuse?
So after a bit of research, a bit of sketching and checking in with Grace (apparently mermaids have green tails and look like Delphi from the Tiniest Mermaid book) I came up with a plan.
The top was a hack of a lined shrug that I already had a pattern for. I just added an organza frill. I haven't worked with organza before, it frays horribly and is too shear to hem nicely. Instead I just folded a long strip in half and gathered it to make the frill. It makes it kind of puffy which I think is a nice effect.
The skirt is just a tube with another organza frill in the seam over the bum and ribbed jersey for a comfy waist band. The bottom is cut into a point at the front and back, I just eyeballed it. The tail fin is a couple of meters of organza doubled over and gathered on to the bottom, then pinched up at the points of the skirt.
The tail was joint effort, my idea wasn't going to work with material that frayed so much, Mark came up with the idea of pinching it up. It gives just the right effect of 'tail'.
So what was the verdict? After asking every morning if I'd made it yet, she was initially very upset that it wasn't a real tail(!) but soon got over it and has 'swimming' around the house for days.