Using a 12lb leader for ladies (of any size) will end with you tying on a new fly... The only time I've ever seen the necessity of that light a leader is when all the bait they're feeding on is tiny - and your fly is small as well...
I've been taking folks fly fishing at night for years - and at times ladyfish (big ocean run ladies...) are our targets when the snook and tarpon are scarce, or having lockjaw. Any small white fly will get bit - as long as it's moving with or across the current. Size your fly to the bait you're seeing in the water. A good all around bug is a clouser on a 1/0 hook in all white (or mostly white). When we're needing ladyfish for bait in the backcountry of the 'glades I use a clouser on a long shank hook, size #1 or 1/0 (Mustad 34011) with the eyes and wing tied in towards the rear of the hook so that we can use a leader without a bite tippet (20lb fluoro, generally...). Catching ladies for bait (live ladyfish are candy for any big fish that swims in the 'glades...) is a daytime gig for me...
Night fishing for us is mostly during shrimp runs and we use the same flies for ladies that we use for tarpon up to about 40lbs. Here's a pic of our go to pattern, the Night Fly....
It's done up on a stout 1/0 or 2/0 hook
I like to have at least a dozen of these on hand for a night trip when it's going off...
Ladies aren't that particular - I'd bet that all white Gurglers and small popping bugs would work for them just fine.... and the strike will get your attention.
By the way, the only reason I tie up white flies for the night scene... is so that my anglers can see them. Pretty sure they'll hit anything that is the right size and moving the way the bait is.
Hope this helps