I dont hear alot about the kinds of shinanigans Allura gets up to in the castleship so i decided i'll just come up with my own.
After Allura awakens from cryo and comes to terms with the state of the universe and her life getting turned upside down (after the drill sergent skit, the castle take over, and launch of the castle) she decides she wants some normality back.
I imagine she was quite rebelious and mischivious back before the war made things so serious, and her mice are completely supportive of her mischief.
The first hints are of course her trying to nudge pidge about her gender, but she gets more crafty when keith talks about bonding moment "trademark" and sees both lance's deflecting and keiths strong feelings about it.
So she makes plans to be their secret wingman cause klance.
She purposely makes their rooms next to each other, pairs them up for training and drills.
SHE IS THE ONE THAT LOCKS THEM IN THE ELEVATOR!
she has the mice spy on them, so she can have updates.
Has the mice steal their stuff to lure them to the other more then once.
The others don't notice at first, lance and keith cause they are really oblivious...
Pidge cause she is focused on finding her family,
Hunk cause he is anxious about the war in general and distracts himself with cooking and tinkering,
Coran notices everything, coran knows all, coran is a spectator, he finds it highly amusing,
Shiro notices first and doesn't really care at first (just imagine, shiro walking by spotting allura spying on klance and just raising an eyebrow at her while she scrambles to pretend she wasnt)
Shiro kinda supports her cause he wants his brother to get a boyfriend, but isnt really actively helping project klance.
Allura ordering keith to go fetch lance after his lion is retrieved.
(just imagine all the convienant klance action that happened in canon is cause of allura, thats the whole fic)
After lance stops trying to flirt with allura we get platonic Allurance. (spa and beauty bonding / girls nights cause pidge wouldnt do it with her)(Shiro gets dragged to a spa bonding night cause he needs rest)
We get platonic Kallura after the marmora/zarkon/shiro missing trainwreck, cause they made up before that battle and are closer after. (Training bonding / enjoying each others company at night when neither can sleep) (Allura and keith finding shiro awake and dragging him to rest)
Lance and keith both thinking the other is either dating allura or wants to date allura and allura trying to use her close friendship to guid them to each other and just not getting through their thick skulls...
Pidge finding out and "helping" (she locks the two in a closet together)
The closet confession works surprisingly...
And it only took allura how many seasons? shrug. I'll let you fill in the details, like whether shiro is a clone or not, whether keith leaves to the blade, how the lion swap effects things and all the juicy drama