Back in the old days when I was 17 I moved out of home into my own rental place. ;)
I didn't share, I was dealing with the difficult fall-out of a dreadful family situation and desperately wanted my own space.
I ended up renting a granny flat - best decision ever! Not too $$ but I had my own space and no more flatmate dramas. If you rent privately (like a granny flat) you'd have even more leeway. The important thing would be to have good refs and be able to prove you can afford it. If a landlord is going to be ultra-picky, they probably aren't worth renting from anyway.
Moving out at 17 was a great decision for me, not just because of my family issues, but in terms of giving me space to grow, managing my own life and really becoming an adult. If she knows you are there to support her I think she's got a great safety net and she'll probably do much better. GL!