Aigoo -- right :) I think the doctors thought she stopped at 12, but Margaret sees this change in her during the Italy stay. ...so we're left to wonder...was it "luv"

or was her mental capacity growing little by little all these years and Margaret was too protective to let that be explored...? Probably some of both actually. Seeing Clara loved by someone else allows her to loosen the reins a bit.
Such real and honest questions for a mother. It begs the listener to jump into Margaret's shoes and think about they would have done.
WickedCatsontheRoof -- the "this is my baby" example is a good one. I guess it just wasn't obvious to me: Haven't you ever been on a vacation or in love or whatever and just wanted to scream from the rooftops? Songs in musicals so often let the characters sing what they'd never say (which is one of my favourite things about musicals)....so again the suspension of disbelief when I heard her sing "we're on vacation". I thought, oh she's just sharing her excitement with us, how nice. (This is actually a family joke as my mom says that all the time when we're on vacation, though admittedly not to strangers

)
Though the realization was earlier, I found "it" *very* obvious though when Clara gets lost and keeps saying her name and street address - probably because she was speaking and not singing, which to me is grounded in the narrative, not just internal thoughts. These conventions of musical theatre can backfire on me