As a Diana 1-Trick since her release, I've run her top for years. I tend to run Mid/Top(Though for a couple seasons I actually ran Top/Mid quite often). It totally CAN work, but with the current toplane meta she just gets smacked more often than not. She can be an amazing splitpusher/Late-mid game beast, but in that long unsafe lane it can be a real problem to get her there.
It can work great, it's just not ideal especially due to the current toplane meta. Back before the mage item changes/Diana number changes/etc when she could rush RoA into Abyssal Staff or Zhonya's to become a good bit beefier I loved running her there though. Lately I've been considering running jungle or even botlane as my second role though. Too many bad matchups top.
(Though, she can be an amazing botlane carry. Pair her with a support who can play safe until 6 and has some good hard CC and it's nasty. Just gotta play super super super safe until 6, and definitely won't work in some matchups.)