Thought I would let you know how I got on.
Turned out that the dress wasn't the dress I though it was. It wasn't a big blousy multi layered tulle dress (just the top later tulle). The skirt was an A line shape, although there was a great deal of fullness. When a huge hoop and added netting was worn with it, it looked ridiculous.
When I pointed this out to the bride and we ditched the hoop and netting, she was much happier with it. Also ditched the bra on my advice.
I cannot for the life of me work out why the shop thought there should be a hoop under it. Apparently, its a shop where you go in and buy the dress there and then and take it away with you. Big change from when I worked with bridal shops and you had to order your dress a year before! I think all bridal shop staff should at least know about how a dress is put together.
So, having done the fitting and being unable to work out where to hem due to all the extra net underneath, I shortened the nine layers to where I thought and allowed a little extra just in case.
Delivered it this evening and it was

perfect

. Happy bride and happy me.