Personally I'd relate Galadriel to the Maia Melian in Doriath from whom she learned and in the 3rd Age acted in like manner.
she remained in the Hidden Kingdom, and abode with Melian, and of her
learned great lore and wisdom concerning Middle-earth. [Of the Return
of the Noldor]
Galadriel has also been compared to Manwë.
Galadriel, the greatest of the Eldar surviving in Middle-earth, was
potent mainly in wisdom and goodness, as a director or counsellor in
the struggle, unconquerable in resistnace (especially in mind and
spirit) but incapable of punitive action. In her scale she had become
like Manwë with regard to the greater total action. [The Istari]
Someone mentioned how Galadriel had a marvelous gift of insight which is true, but the darkness she saw in Fëanor she failed to see in herself:
she did not perceive that the shadow of the same evil had fallen upon
the minds of all the Noldor, and upon her own. [The History of
Galadriel and Celeborn]
Elven magic is innate and can be bettered with practice. The use of devices, like the Rings of Power, can impede the development of these innate abilities. Tolkien speaks about the use of these devices
for power, for making the will more quickly effective, - and so to the
machine (or Magic)... all use of external plans or devices (apparatus)
instead of development of the inherent inner powers or talents - or
even the use of these talents with the corrupted motive of dominating
Such things "make the will more quickly effective" [Letter 131]. When she showed the Hobbits some her ability, which they understood as magic, she said:
this, if you will, is the magic of Galadriel. Did you not say that you
wished to see Elf-magic? [The Mirror of Galadriel]
This is with her use of the Mirror to allow Frodo and Sam to see things. What she says about it is that:
Many things I can command the Mirror to reveal... to some I can show
what they desire to see... the Mirror will also show things unbidden,
and those are often stranger and more profitable than things which we
wish to behold. What you will see, if you leave the Mirror free to
work, I cannot tell. For it shows things that were, and things that
are, and things that yet may be. [The Mirror of Galadriel]
According to Tolkien Elvish
"magic" is Art, delivered from many of its human limitations: more
effortless, more quick, more complete (product, and vision in unflawed
correspondence)...the Elves (the representatives of sub-creation par
excellence) [Letters of J.R.R. Tolkie, Letter 130]
There is an example I think of what Tolkien refers to as "goetia" where the Elvish minstils are known to "make the things of which they sing appear before the eyes of those that listen." [Appendix A: Tale of Aragorn and Luthien] In Letter 155 Tolkien says the Elvish
goetic effects are entirely artistic and not intended to deceive
whereas with Sauron he uses
goetia to terrify and subjugate.
In either case, with the Elves or with the Enemy Magic is used for "immediacy: speed, reduction of labour, and reduction also to a minimum (or vanishing point) of the gap between the idea or desire and the result or effect." [Letter 155]
I think Galadriel has honed her talents and can use them as good as anyone. One more example of Galadriel perhaps using magic would be to look at her brother Felagund who dueled Sauron. When they fought Finrod's guilt weakened him before Sauron.
He chanted a song of wizardry, Of piercing, opening, of treachery,
Revealing, uncovering, betraying. Then suddenly Felagund there swaying
Sang in answer a song of staying, Resisting, battling against power,
Of secrets kept, strength like a tower, And trust unbroken, freedom,
escape; Of changing and of shifting shape, Of snares eluded, broken
traps, The prison opening, the chain that snaps.
Backwards and forwards swayed their song. Reeling and 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 sighing of
the Sea beyond, Beyond the western world, on sand, On sand of pearls
Then the gloom 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. [Beren and Luthien]
Even against Sauron one on one he began to gain the upper hand before his guilt did him in. This might be an example of goetia in action.
The extent of Galadriel's powers? I'd say her peak is quite high as she is often compared in terms of her gifts with the greatest of the Children of Illuvatar, Feanor. C.T. says of a late note his father wrote, "he emphasized the commanding stature of Galadriel already in Valinor, the equal if unlike endowments of Feanor" [the History of Galadriel and Celeborn].