Clientele is singular: a 'grouping' term like 'flock' or 'horde' that lumps multiple individual units into a single term. So, "During its heyday, the shop's clientele was representative of the finest in high society."
Mice is plural.
Singular: city Singular possessive: city's Plural: citiesPlural possessive: cities'
Singular (present and past)
Who may be singular or plural.
The pronoun she is singular; if there are two or more females, the appropriate pronoun is they (subjective) or them (objective).