MrsD, I can't imagine how someone would get Debbie from your name! 
MrsMangelfanciedPaulRobinson, her dad does it to start a rough and tumble session with her, she's not doing it to be violent as it's totally not in her nature, she, like many children, likes to roll around with her dad. As I said before my second child is ex-IUGR (so very tiny and not able to take a lot of rough play) and my third is only 16 months old and all of them join in on the beating Daddy up game. The response to it outside the family is because she won't say anything, it's a frustrated sigh. Doesn't come across to me when I've seen it as "madam-ish" and it's not something anyone would ever accuse her of.
We gave her her name because it's a beautiful name, my family has a few people who have names that can be shortened and never were, we have always said if she chooses that name for herself then that's her choice. If someone introduced themselves to me as one name I would find it rude to call them something else unless they said, pinching someone else's example, "I'm Samuel but everyone calls me Sam". My mum has a shortened name, some people insist on lengthening it to it's full name (although there's a few options, they don't usually bother to find out which one it is or if it is) that's rude too. I'm shocked that there are people here who would be that rude 
We have given her tools to deal with it, we've told her she can tell people she prefers to be called by her name and as the shortening sounds like a question we've told her ways to answer the question. We've talked about how it's rude to call someone by a name they don't like, I compared it to her nanny how if she tells people her name is that then it's rude to call her by her full name, she has been told that it's not rude or naughty or going to upset people to tell them she doesn't like it. The TA obviously KNOWS that she doesn't like it to turn around and say "I have to call you that because your name's too long" I don't know if that's because she did stand up for herself or because the other teacher told her. To be honest I think explaining it like that is ruder than assuming you can call someone something other than the name they were introduced to you as. I wonder how many people would be happy and not find it rude if their boss said "Sorry but this is a busy office so I'm going to cut your name down to save time, those milliseconds add up"?
Arisbottle - I didn't contact the head, I was talking to her Y1 teacher who is a senior teacher (like deputy-deputy head) about a different issue and mentioned it to her.
3monkeys3 - other than with her dad (which is the game really) she is good about it, it gets to her and she never mentions it and it seems that only people who don't use it actually notice she doesn't like it.
I'm looking forward to my second daughter going to school next year, she has a Welsh name, not so uncommon that you don't know it (there's a few famous ones) but she gets some interesting spellings, masculine form and whilst we're trying to teach her to recognise her own name, everyone else uses the lazy spelling. My eldest could write both names before she went to school but I can see it being harder to teach her sister.