She should have her own key, but I understand your worry considering you suspect she spends her money on drugs.
I will say that it depends on what 'drugs' she's spending her money on as to whether you are reasonable or not.
At 17 I had no 'curfew' I was simply expected to be quiet. I was also working and paying my mum my 'keep' (not rent, just a few quids contribution).
She probably winds you up until you react badly. I didi the same to my mum, she hit me, she is THE most placid person on the planet, but she knew my buttons and pressed them hard out of frustration, I reacted, I pushed her back, she hit me... I hit her once, horrible.
I think you need to meet in the middle somewhere. She isn't your baby anymore, she needs her freedom and key, she needs to know you won't be waiting up half the night until she's home. You need to know she's safe.
I also stole off my mum. She had to lock her bedroom door... it wasn't just cash it was lipstick, clothes, everything... I am not proud 20 years on, but even though it was unjustifiable, even though it was wrong, I can still remember me feeling justified because my parents assumed a lot, judged a lot and listened little. I was a real emo teen who was angry that my parents didn't at least TRY to understand.... not saying that's you, but it sounds like you clash enough for it to be similar.
It really does depend on the 'drugs' she's taking and how much she's stealing as to how far you go at tackling this. Either way, she needs no curfew and a key. Zero tolerance on the stealing. She needs to pay you 'keep'. The mistakes she makes you cannot avoid, and will only exacerbate if you keep that 10.30pm curfew, but you don't have to tolerate her stealing from you.