Valkyrie is, (more or less), a well-rounded legend between assault, skirmisher, and recon, as her tactical makes her great for assault, her jets makes her great for moving around, and her ultimate, (and threat vision), is great for recon.
I suppose she could also be supportive, as her ultimate can save the team from a lot of situations, (such as getting past a team that's gatekeeping the zone), but she's not very good at holding any ground as a controller, (however her tactical can make enemies fall back and thus delay an attack for a few extra moments).
Personally, I think her place as a recon legend suits her the best, as it didn't make much sense to have her as a skirmisher, outside being able to fly around, (which considering that anyone can use EVAC towers), it was only her jets that set her apart from the others as a skirmisher.
In short, her kit, (in my opinion), is best suited for recon.