She and Signum are probably one of few Nanoha characters that might possibly qualify as GAR.
Take Nanoha her self for instance. Powerful as hell, tough as nails, and capable of kicking all kinds of ass. None of those things in and of themselves are GAR, awesome yes, GAR no. Nanoha is very feminine, still very much a girly girl.
Now Subaru is masculine as hell. With that picture of the transformations of the cast with Kenshiro thrown in, Subaru's pose and stance look almost exactly like Kenshiro's. She is woman who is almost manly. If you met her in a bar or something, you would find her so manly you would doubt your own masculinity.
Now if you rely on the "must have a penis to be GAR" rule, she's out. (Doujins don't count.)
But if you go with GAR as admiration for masculine badassery, she probably counts.