Hi Travis,
Well, here's what the Oxford English Dictionary knows about flabberg(h)asted:
First mentioned in 1772 as a new piece of fashionable slang; possibly of dialectal origin; Moor 1823 records it as a Suffolk word, and Jamieson, Suppl. 1825, has flabrigast to gasconade, flabrigastit worn out with exertion, as used in Perthshire. The formation is unknown; it is plausibly conjectured that the word is an arbitrary invention suggested by flabby of flap and aghast.
Eric Partridge's etymological dictionary also sees it as a combination formed from flabby and aghast, the idea, I suppose, being that one is made limp (flabby) by being in such shock (aghast).
The OED and Webster do not offer
flabberghast as an alternative spelling, but
flabberghasted generates about 17,000 hits on Google, compared to over a million for
flabbergasted. I'll leave it to you and your friend to decide whether any of this makes her spelling "accepted"
