Hmmmh, regarding pitches and musical brain-ing, I
might have an idea (though I'd recommend you discuss anything you do with your teacher):
I had a self-styled "solfege"-exercise ("Gehörbildung" - lit. "Hearing-development") I trained way back before I tried out for academy (bass, though): Singing intervals - i.e. two notes after another - and trying to recognize the interval, the "tonal distance", between them. I'd make myself
'Interval-Mnemonics' out of the first two notes of melodies of songs I knew well, for example:
Octave -
Somewhere over the Rainbow (Some-where - that's the octave)
Fifth-
Star Wars ThemeTritonus - Maria, West Side Story (In the chorus, the "Ma-ri" in "Maria" is the tritonus)
Fourth - Police Siren (That's German patrol cars, though)
Major third -
Oh when the Saints ... (C-E-F-G If you leave out the third note, you have all the notes of a
major chord)
Minor third -
'Georgia on my mind' or 'Save the best for last'! (Both start with a minor third, but "Georgia" is in a minor key, while "Save ..." is in a major key. If the key of "Save ..."was "C" (cf. spoiler), you'd start with E (major third), then G (fifth). Choose what you find more convenient)Major Second - do-re! (Can you sing a major scale?)
...
Once you're comfortable with singing the interval 'upward', sing it 'downward'. Then let your wife sing you an interval & try naming it. Stuff like that - make a game out of it.
Keep it
playful - Fear is the mindkiller!
Problems so far include poor posture, an intermittent ability to match pitches, and self-consciousness. There is a humiliating inability to concentrate on more than one thing at once -- if I get one thing right, something else falls apart. If there is such a thing as a music brain, I don't have one.
Self-consciousness: Well, ask Meryll Streep how she feels just before her part starts (Hint: She
still gets nervous). Maybe you have more music in your brain than you think? Methinks you wouldn't be so frustrated otherwise - the
really 'music-blind' people smile at you while singing a half-note off-key (*shudder*)
EDIT: Here's the "Saving the best for last" written out:
You don't have to read it - just note that there's no # or b's. Meaning: You could play the entire song using only the white keys on a piano. The song is in a 'major scale'. Now, you might think that's news for your ear, but it isn't. The entire 'western' musical system, back to the ancient Greeks, is based on those seven notes, the so-called 'ionic/major scale'. You've heard this a bazillion times - so you 'know' the notes without knowing. It's what you'd instinctively use if you just started humming
"random (ballad) stuff that sounds good to me".
EDIT II: Maybe
https://www.sheetmusicdirect.com/se/ID_No/23776/Product.aspx helps - you can change the key (the "base note") with the button "transposition" (Ask your wife what key you're supposed to sing it in). Advantage: You can let it play the notes for you, in the key you'll actually use, at a tempo of your choosing.