I tired looking up "seven-five" tones:
https://en.m.wikipedia.org/wiki/Seventh_chord
Assuming the source and what Rosa is analyzing are related, this would make her a prodigy on par or even greater than Mozart/Beathoven.
If true, what she refers to 7.5, is probably the tone of a Major seventh chord accompanied with a perfect 5, or just a blind attempt to map out Alina's general tone. At least that's as far as I could grasp when she suddenly brings up 5.7.5.
I think the takeaway from this at least is to show off Alina's creative acting prowess, in which case, only serves to show the depth of Rosa's restraint; a person with such deliberate control in their speech just out of reach for our dear rottenness.