It all depends:
on the school
on the cohort applying for a scholarship
on whether your dd has a musical aptitude
on whether she will want to apply for a scholarship
usually for a music scholarship you would present 2 instruments (one can be voice), but it isn’t done on grades alone, the scholarship day can be tough. My dd (presented cello/piano, but would now - 4 years later - present piano/voice in all likelihood) had to: prepare pieces in her chosen instruments. Play as part of an ensemble comprised of the ragtag lot that turned up for scholarship entry (so varied instruments - from cello to flute to harp plus voice etc), sight reading her part; had to arrange an instrumental piece as part of a group - this was set up so that the best arrangement meant each participant played their second instrument; an interview about her music interest and accomplishments; plus various other musical tasks over the day.
dd was grade 4 cello (age 10), which is a tough grade threshold (apparently - her teacher was delighted with her exam result) and grade 3 piano, but her ability in both instruments was a lot higher, she just had trouble taking the exams (ASD). She got her scholarship.
music scholarship is an odd one to be aiming for from initial music lessons, though. So much changes over the years at primary school - you might as well be aiming for an art scholarship, or a drama one (and why not an academic one?) at age 6. You really can’t tell what’s going to happen (dd would now enter for a drama scholarship rather than music, if she were to take the assessments now).
at age 6, I would have said ds would enter for an art scholarship(if I’d had to name one), but as it happens he will enter for drama (if he chooses to, still undecided)