I would do something similar to this. I think with teens (admittedly I have teen boys rather than teen girls, but the principle is probably broadly the same) there are times to confront, and times to be rational/reasonable, and times to simply explain that actually if they can't behave in a respectful manner then you'll have to take action to ensure that things are taken care of.
So a small box or case that you keep your expensive products in, get a big chunky padlock with a combination lock so DD cannot access them. Explain to her that yes, this probably does seem pathetic, and petty, but unfortunately she has demonstrated that you cannot trust her, and so given that you don't have endless money to replace expensive things, this is how it has to be. Add anything that you don't want her to use (makeup, jewellery, whatever) to the box.
I wouldn't necessarily insist that I take her pocket money, but I'd offer her the option of using it to pay you back if she wants to. Alternatively she can get cheap shampoo from Poundland for however many weeks/months it takes for you to recoup your £40, rather than her getting anything more expensive. No other hair products at all.
The Disney Dad problem is unfortunate, but if DD is hoping to go to university one day it's definitely worth having the conversation around learning to be respectful to others, and their belongings, and making sure she doesn't end up being the flatmate that everyone loathes and despises for being an inconsiderate little brat. Disney Dad won't be able to fix that one for her, no matter how many expensive toys he replaces.