Also for future reference, i assume she called him 'onii-san' as an address/honorific but "mister" might be more fitting than 'big brother' since it's probably intended to be distant/calling him older than "big brother" which might be more endearing, although i know both technically fit, if not just leaving it in JP like "Onii-san" (or maybe 'young man' but that'd be more fitting if an older lady called him that [tho i imagine someone older would call him something else tho idk if there's a male equivalent to Ojou-san/ojou-chan lol])