After the story made headlines this morning, a Facebook conversation has emerged in which Ms Lawrence explains her actions.
It begins with Tanya asking about what happened - below are some extracts form the lengthy chat.
She wrote: "I was very shocked to see the invoice in Alex's school bag. I did not realise that you had to pay for each child, as you never mentioned anything about money when we spoke....
"I apologise for not letting you know, but I did not have a phone number or an e-mail for you to let you know the situation (I also didn't know your first name, or I would have looked you up).
"If I had known that I would have to pay if Alex did not go, then I would have paid you the money, no problem. I do not like fighting with people, and would prefer to settle this amicably."
Julie replied: "I didn't mention the money when we spoke because it was a child's party, it doesn't matter if you have to pay per person or for a group if people agree to going.
"I confirmed that with all parents on the Thursday before the party that they were going as I had to pay that day, and Derek told me Alex was looking forward to it and would see us there, to me that is confirmation.
"My phone number was on the invitation that was sent out to Alex...
"This is not the first time Alex has not turned up to a party that he has been invited to, either. The amicable way round this I believe would be to pay me the money and let a lesson be learnt, I hope this is agreeable ?"
But Alex's mum was not pleased with the response, explaining that she wasn't aware of another party he hadn't turned up to. She added that the school wasn't happy that the envelope had been placed in her son's bag.