I would asked to have this moved from AIBU where everyone will have you kick your child out/leave the bastard and will eat/spend/heat 100 times less than you do. Have it moved to the SEN board where you're more likely to get some help and support from people who understand what it's like to be ND or have experience with handling ND children.
People with ASD can often come across as entitled because they struggle to put themselves in any one else's shoes. It's very likely that she is emotionally up to 3 years behind her peers - you should think of her as basically a 15 year old.
It's fantastic that she wants to join the police, please, please support and work with her on that - what could she do in the meantime that will boost her application? She probably has low self esteem already, and the rejection on the first attempt she probably took very hard and now feels even more worthless. She desperately needs your support not to tell her she has to leave if she doesn't do what you want. She won't see the point in doing some random job if she wants to be in the police and probably feels like a complete failure. What she needs is lots of help and support to get her back on the right road and believing that she can get in the police, she just needs to do x, y and z to help. Talk to her about how when you apply for jobs if you have holes in your cv that it doesn't look good, you need to have been doing something, short courses, working on her fitness (if that's still important for joining police), working to show she is punctual, reliable, helpful etc
I was your dd and I ended up marrying someone I really shouldn't because my parents were like you, I really needed help and support at that age, I felt very lost and struggled with executive function, the 'busyness' of places and people, the expectations of my parents and low self esteem. I promise you that she needs your support on the next steps and how to move on from this disappointment not your anger and being told she has to leave.