Reflexive verbs in passé composé agreement

Question

I know that all reflexive verbs are conjugated with être in the passé composé, and that the past participle agrees with the subject in number and gender. I learned that when there is another object present (a body part in all or most cases) there is no agreement.  In an A2 test, I answered "Elles se sont brossé les cheveux." and was marked wrong, with "Elles se sont brossées les cheveux." as the correct answer. I asked this question on the quiz question site and was redirected to this Q and A board. Thanks for your help/clarification.   -- Bonnie Christianson

Answer

Elles se sont brossés, cette phrase est feminin et pluriel, et par conséquent en devient "se sont brossées"
I hope this helps

Answer

Merci pour la réponse, Ron.

Ce n'était pas "Elles se sont brossées." mais "Elles se sont brossé les cheveux." Voici une explication de Laura Lawless de "Lawless French" (et kwiziq.com) :

When there is no preposition in front of the noun, the noun is direct and the reflexive pronoun is indirect.

Elle s’est rasé les jambes.	 	She shaved her legs.
Elles se sont lavé les cheveux.	 	They washed their hair.

It would seem to me that my example would be quite similar to the second example that Ms. Lawless uses, so I still have my question : Why is the answer "Elles se sont brossé les cheveux." incorrect? Merci pour votre aide.  -- Bonnie Christianson