She is asking how she can teach her mother and sister about the rulings on tahaarah (purification)
Question

                My question is about my little sister. When her menstruations start, should I be the one to tell her about ghusl and stuff (cause Im pretty sure that my mom doesn't know about that stuff ...)? And should I explain that stuff to my mom also? It would be really akward cause I'm the child and she is the mom..

How could I talk them about it?

Also I want to ask: If someones menstruations haven't started yet, but she's having vaginal discharge, should she do ghusl? Because she would have to do it many times a day because of it.
Praise be to Allah.
    Firstly: 

    There is no doubt that teaching children 
    what they need to know about their religion comes under the heading of 
    obligatory education and care that Islam has enjoined upon parents towards 
    their children. Allah, may He be exalted, says (interpretation of the 
    meaning): “O 
    you who believe! Ward off from yourselves and your families a Fire (Hell) 
    whose fuel is men and stones” 
    [at-Tahreem 66:6]. 

    Mujaahid (may Allah have mercy on him) said: 
    Fear Allah, and advise your families to fear Allah. 

    Qataadah said: He should instruct them to 
    obey Allah and tell them not to disobey Allah, and he should discipline them 
    in accordance with the teachings of Islam, and he should enjoin them to 
    follow the teachings of Islam and help them to do so. If you see any act of 
    disobedience towards Allah, then you should make them stop it and rebuke 
    them for it. 

    Something similar was stated by ad-Dahhaak 
    and Muqaatil: It is the Muslim’s duty to teach his household, both his 
    family members and his servants, what Allah has enjoined upon them and what 
    Allah has forbidden to them. 

    Tafseer Ibn Katheer, 
    8/167 

    The Messenger of Allah (blessings and peace 
    of Allah be upon him) said: “Each of you is a shepherd and each of you is 
    responsible for his flock. The ruler of the people is a shepherd and is 
    responsible for his flock. A man is the shepherd of his household and is 
    responsible for his flock. A woman is the shepherd of her husband’s house 
    and children and is responsible for her flock.” Narrated by al-Bukhaari 
    (853) and Muslim (1829). 

    He (blessings and peace of Allah be upon 
    him) also said: “Your child has a right over you.” Narrated by Muslim 
    (1159). 

    An-Nawawi (may Allah have mercy on him) 
    said: ash-Shaafa‘i and his companions  (may Allah have mercy on them) said: 
    Fathers and mothers are obliged to teach their children that which will be 
    obligatory upon them when they reach puberty. So the parent or guardian 
    should teach them how to purify themselves, how to pray and fast, and so on; 
    they should teach them that fornication and adultery, homosexuality, 
    stealing, consuming intoxicants, lying, backbiting and so on are all haraam; 
    they should teach them that once they reach puberty, they will become 
    accountable, and they should teach them how to recognize when they have 
    reached that stage.

    End quote from al-Majmoo‘. 1/26; see 
    also al-Majmoo‘, 3/11 

    Secondly: 

    If your mother does not know the rulings 
    connected to reaching puberty, as often happens in places that are far away 
    from knowledge and scholars, such as desert regions, Western countries, and 
    so on, then the mission of teaching and calling people to Allah must be 
    undertaken by whoever in the family has that knowledge, whether that is a 
    boy or girl, the closest, then the next closest. 

    So long as you have some knowledge of the 
    Islamic rulings that are needed, and you know that your sister is about to 
    reach puberty, then you must teach her what she needs to know of these 
    rulings, and you should choose the best and most appropriate way of doing 
    so. 

    In fact, we think that your teaching her may 
    be more beneficial and easier than the mother teaching her, because of your 
    closeness in age and because you will understand one another easily. 

    Then you should also teach your mother what 
    she needs to know of religious rulings that you think she does not know. 

    You can also seek help in doing that, along 
    with direct teaching, by telling your mother about beneficial Islamic media 
    channels, such as trustworthy educational websites and good Islamic 
    satellite channels that follow the way of Ahl as-Sunnah, if there is 
    something that will benefit your family in a language that they know. 

    There is no need for any shyness or the like 
    in any of these matters. There are still people who do not know many rulings 
    that they need to know, and the one who knows them is obliged to help them 
    to learn them, whether they are young or old. 

    It was narrated from Zaynab, the daughter of 
    Umm Salamah who said: Umm Sulaym came to the Messenger of Allah (blessings 
    and peace of Allah be upon him) and said: 
    O Messenger of Allah, Allah is 
    not too shy to tell the truth. Does a woman have to do ghusl if she has an 
    erotic dream?...

    Narrated by al-Bukhaari (130) and Muslim 
    (313). 

    An-Nawawi (may Allah have mercy on him) 
    said: 

    She only said that as an apology before 
    asking her question, for which there was a need, because it was something 
    that women usually feel shy to ask about and mention in the presence of 
    men. 

    This shows us that it is appropriate for the 
    one who has a question to ask about it, and not to refrain from asking out 
    of shyness. That is not really shyness, because all shyness is good and 
    shyness does not lead to anything but good, but refraining from asking in 
    this case is not good, rather it is bad, so how can it be shyness? … 
    ‘Aa’ishah (may Allah be pleased with her) said: How good were the women of 
    the Ansaar; shyness did not prevent them from understanding matters of their 
    religion. And Allah knows best.

    End quote from Sharh Muslim. 

    Thirdly: 

    The vaginal secretions that come from women 
    several times every day do not require ghusl; rather ghusl is only required 
    in the case of janaabah (impurity following sexual activity) or when a woman 
    becomes pure following her menses. 

    For more information, please see the answer 
    to question no. 50404. 

    See also the answer to question no.
    99507 for information on the difference between 
    maniy, madhiy and other secretions. 

    And Allah knows best.