Well, Galadriel would engage Balrog in magical battle and would have a pretty good chance to win, remember how her brother Finrod Felagund dueled Sauron?
"He chanted a song of wizardry,
Of piercing, opening, of treachery,
Revealing, uncovering, betraying.
Then sudden Felagund there swaying,
Sang in a song of staying,
Resisting, battling against power,
Of secrets kept, strength like a tower,
And trust unbroken, freedom, escape;
Of changing and shifting shape,
Of snares eluded, broken traps,
The prison opening, the chain that snaps.
Backwards and forwards swayed their song.
Reeling foundering, as ever more strong
The chanting swelled, Felagund fought,
And all the magic and might he brought
Of Elvenesse into his words.
Softly in the gloom they heard the birds
Singing afar in Nargothrond,
The sighting of the Sea beyond,
Beyond the western world, on sand,
On sand of pearls on Elvenland.
Then in the doom gathered; darkness growing
In Valinor, the red blood flowing
Beside the Sea, where the Noldor slew
The Foamriders, and stealing drew
Their white ships with their white sails
From lamplit havens. The wind wails,
The wolf howls. The ravens flee.
The ice mutters in the mouths of the Sea.
The captives sad in Angband mourn.
Thunder rumbles, the fires burn-
And Finrod fell before the throne"
Given the fact that Galadriel lived much longer than Finrod, was tutored by Meliana, her reputation, presence, and Balrog being weaker than Sauron I think that they either would both die or Galadriel would barely win.
What do you think of Ringwraiths versus Balrog, remember that Witch-King had the power to oppose Gandalf The White( or so he thought).