First, great job on your first 'stranger' cake! (sometimes it makes ya wonder why we sell to these 'strange' people, doesn't it?
Second, if the son's bday and all the memories of his bday will forever be ruined, let's pause for a moment to feel sorry for this poor child - what a miserable existance he must live ( yeah, I think mom went a little off the deep end)
Third, since you made the cake and you decorated the cake, it rightfully belongs in your portfolio (you could always chalk a page up to 'pissiest customers' and put her name in there to make her feel special - no lying or cheating there!)
And if she wanted a cake shaped like a jersey that bad
, all she had to do was take a little kitchen knife and carve around the jersey you had on her cake! Problem solved
Good to see you don't let it get ya down!