I've been playing Luna recently and I thought of some minor kit adjustments that might not necessarily make her more powerful, but add a bit more potential to her kit.  
  
Smooth Skate should be changed to be active all the time. The amount of speed while in combat should be reduced, but I think her skating around quickly is a fun part of her kit and it would be really good if you could do it while fighting. I think you also might need to reduce her health to 250 to compensate for the movement boost.

I think the one minor change to her Snowflake is that allies with it also get healed when she deals damage. I like how Adam and Mantis have playstyles that reward hitting shots and I think it might nice for Luna to have this as well since her kit doesn't offer much utility or have the high damage of Ultron.

Remove Self Snowflake. I don't think this adds much to her kit and I think the above mentioned buffs would balance the loss of this ability.

This final adjustment can't happen in a vacuum and would need to happen along with game wide changes to a bunch of other stuff. Keep everything about her ult the same, but make it 6 seconds long (also maybe remove the on heal cast and shield gained).

Luna Snow Adjustments ideas