Translation:They brush their hair in the bathroom.
Funny, this is the second time I heard the initial "ellas" as "ella" and it throws my hearing of the rest of the sentence off. Can't quite understand the syllables I'm hearing. Afterward, when I know it's "ellas", the rest of the syllables make sense to my ear. I can hear the "an" as part of "cepillan" and not as a separate word "en".
Spanish looks at this situation differently from English.
In Spanish, when a group of people each has his/her own of an item (even body parts), that item is singular.
The Spanish looks at the number of items per person.
In English, we look at the total number of items and use the plural.
These are different perspectives but equally valid.
Ieoum, in English you have to specify whose body part you're ... acting on, since English doesn't have the luxury of adding object pronouns to its verbs. So while in Spanish you say "Se cepilla el cabello", you can't say "She brushes herself the hair". "Herself" doesn't work here, so you need to specify the target with a possessive form: "She brushes her hair."
Clear evidence that I need to dig more deeply into grammar. I would have thought the sentence should read, "Ellas se cepillarse el cabello" since cepillar is a transitive verb and cepillarse is a reflexive verb. Just when I thought I was beginning to understand Spanish grammar....