So how do I make 4yo DD a mermaid's tail

[Coveredinweetabix]

DD is off to a birthday party in 10 days time at which the theme is "under the sea". Whilst I'm delighted the host has chosen something other than princess or pirate it does mean I'm going to have to make something and my skills are pretty limited. I rashly promised to make DD a mermaid's tail this evening and she is very excited so how do I do this? Or do I come up with a plan B? I have a Hobbycraft, John Lewis & independent haberdashers nearby. I don't have a sewing machine. Not only do I have to come up with a plan for the tail, I also have to work out how to attach it to her. Over the shoulders or belted?
Any help would be much appreciated.
Thank you

Not sure if this will be much help as it's sewn. Is there anyone you could borrow a machine from or could you hand sew?

tootsiegrace.blogspot.co.uk/2009/10/make-it-sparkly-mermaid-tails-tutorial_05.html?m=1

www.ikatbag.com/2012/03/listen-to-children-mermaid-tale-er-tail.html?m=1

You might get an idea here?

Don't know if it's a little late for this - DD has one that my mum bought her that would be fairly simple to replicate. Basically it's a big triangle (point downwards to the floor) with fins on the bottom point and ribbon coming off the two other points. You wrap it round with the 'fin' at the front and tie the ribbons in a bow at the front of the waist (or chest depending on how tall the child is who's wearing it). It has frilly bits along the two edges that aren't on the waist so it looks a bit prettier (but they wouldn't be necessary at all), and a separate vest type top that you wouldn't need to do for a one-off party?