Daughter's unreasonable demands and unwise choices

[Smileatalltimes]

I feel like I'm continually disagreeing with my 16 year old daughter and saying no to her demands, which is making her extremely hostile.
Latest examples:
Not agreeing to pay for her to have her hair dyed black at a salon.
Not agreeing to pay £250 deposit for a 6th form trip (plus subsequent payments) when we don't know at this stage if she will qualify for 6th Form.
Refusing to pay £200 for a prom dress on Vinted (might not fit).
Not supporting her A level choices. She's refusing to take her best subject, which could lead to various careers I think she'd enjoy, because she doesn't like the teacher. Instead she's selected only creative subjects which she enjoys but doesn't want to do as a career (eg: Dance & photography) this is the most serious current conflict & I could really do with some advice on how to handle!
Generally she's not a bad teen, doesn't get into much trouble at school, is fairly focused on her studies, but these (seems like daily) battles are getting me down.

oops a couple of grammar/typos in that post apols!

Be very careful, you’ll lose her.

No, you won't, it's typical teenage unreasonableness, you're right to not bend to her every whim. She needs to learn the value of money.

You've pointed out the downsides of the A level choices and of the Vinted dress being non refundable. What's important is if she goes ahead and chooses the wrong A levels, buys the dress and it doesn't fit is that she owns her mistakes ... you don't bail her out. Don't pay the deposit and she needs a job if she wants a salon job, it's not as some ridiculous poster says, spiteful not to say she can have all this ... it's about learning you need to work for adult treats.

I actually think it’s really commendable that she is looking for and found a prom dress on Vinted. So much fast fashion for proms this is a sustainable and earth-friendly option.
ask the seller to send measurements of the dress before buying. You could always make them an offer that’s less than asking price.
A deposit for a school trip is presumably refundable up to a certain point- I’d clarify with the school and pay it.
changing hair colour dramatically is a lot of upkeep I’d price it at the hairdressers and discuss the upkeep necessary with hairdressers so she realises it may be cost prohibitive.