I'm sure one of the booties will be along and confirm I'm no expert on Booty dresses. I personally never seen a Booty in blues at a passing out parade only seen them in Lovats even the drill instructors
Wear what you like, it's her day, all eye's on her. If you want to go in civvies do it. Go in rig and you'll end up in Navy News as a feel good factor phot opportunity but it's your call. Been on a few Raleigh divisions and only ever seen Booty guests in lovats (unless your a bandie, what instrument do you play Royal )
Just checked with an oppo of mine who happens to be the Base Warrant for Raleigh and he said the official line is serving personnel attend in best bib and tucker with medals (blues) or attend in civvies as no-one will be any the wiser, hope that helps.