Why do you use the word "se" as in Ella se lava el pelo. Why can't you say "Ella lava su pelo?"
Why do you say "Ellas se lavan los manos" instead of Ellas lavan los manos?
Why do you say "Estoy en el bano porque me estoy lavando los manos?" Why is the "me" in there; isn't using Estoy enough?
I don't understand why you add "se" and "me".
I think an important thing to remember is that the objects in all of your sentences lack owners. Translate what you said directly to English: Ellas lavan los manos -> "They wash the hands."
In English, that makes no sense for the same reason that it makes no sense without "se" in there - you have no idea whose hands they're washing. You would ask, "The hands? Whose? Their own?"
As you learn Spanish more, you'll discover that they tend to over-specify objects and recipients of actions much more than we do in English. We assume and take context for granted a lot more than we realize.
Hi Vkg and Welcome to the forum
the verb lavarse is reflexive so the se part is an essential part of the verb.
Reflexive verbs show that a person does an action to themself/herself. Leaving out the reflexive pronoun would cause some of the meaning to be lost !
eg: Se lava su pelo = He washes his hair
or your example: Se Levan las manos = They was their hands
I hope that this helps clarify the situation
If you would like to gain further understanding of the subject I sugeest you follow Nametaken's excellent link to Paralee's video lesson on Reflexive verbs and the morining routine
As nametaken has said if you leave out the reflexive me, se, etc you have as in your example
Ellas lavan los manos - They (females) are washing the hands (of their children, their husbands, etc)