Now. from what i have gathered, I'm going to make an argument.
For one, GV has definitely had a lot of experience dodging Danmaku, a ton. Slave Arrow may work a couple times (not sure, GV may be able to dodge all together), since a Danmaku is still a Danmaku. From this, she will definitely get a few solid hits in. IF she can consistently hit these attacks through S. Arrow or Melee Attacks (I'm assuming she has the capability to deal with range and close the distance), she might be able to get a win. Her CQC is definitely going to be an edge if she gets close, and knows when to back out (that is, if she knows Gunvolt's sudden Astrasphere and Anti-CQC comes in)
However, Gunvolt again, will be able to dodge the S.Arrows with Danmaku experience. Thus, Boa should be able to do something else instead of just spamming S.Arrows which GV will eventually get the hang of dodging. The bad news is that GV has a LOT of Anti-Range and a Danmaku of his own in Voltaic Chains. Astrasphere is basically one giant orb of "Fek everything near me". And Boa is going to have to deal with Gunvolt's Galvanic Renewal, reseting all of her progress. Septimal Shield will half the damage he takes, Septimal Surges doubles it. If Boa gets tagged, which is especially easy with Orochi's Danmakuish capabilities, the Flashfield is gonna be doing hefty damage.
Gunvolt, Mid Difficulty, Boa is dangerous, but not something as bad as what he has already faced, specially after he fought Elise