I think a lot of Somalis are suffering with siblings who are atheist, agnostic or just munaafaqs and it's a tough thing to deal with. There is an agenda to turn people away from Islam, in particular, the women, by making sure that certain voices are amplified. These amplified voices belong to misogynist cavemen who claim to be Muslim that like to tell the world that Muslim women are 'property' etc, etc.
This means a girl or a woman, with no firm understanding of Islam, will think she needs to 'liberate' herself from this 'tyrannical, patriarchal religion'.
I'm currently dealing with the situation you described and Wallahi it's heartbreaking especially the toll it takes on our righteous mothers. I can't even begin to describe the lengths my mother was willing to go for my sibling. I gave her a piece of advise that put her heart at ease for the moment. Remember this simple thing :
Al-Qasas 28:56
You surely cannot
guide whoever you like ΛΉO ProphetΛΊ, but it is
Allah Who
guides whoever He
wills, and He knows best who are ΛΉfit to beΛΊ
guided.
Fatir 35:8
Are those whose evil-doing is made so appealing to them that they deem it good ΛΉlike those who are rightly
guidedΛΊ? ΛΉIt isΛΊ certainly
Allah ΛΉWhoΛΊ leaves to stray whoever He
wills, and
guides whoever He
wills. So do not grieve yourself to death over them ΛΉO ProphetΛΊ. Surely
Allah is All-Knowing of what they do.
Al-An'am 6:125
Whoever
Allah wills to
guide, He opens their heart to Islam. But whoever He
wills to leave astray, He makes their chest tight and constricted as if they were climbing up into the sky. This is how
Allah dooms those who disbelieve.
Al-An'am 6:39
Those who deny Our signs are ΛΉwilfullyΛΊ deaf and dumbβlost in darkness.
Allah leaves whoever He
wills to stray and
guides whoever He
wills to the Straight Way.
Ibrahim 14:4
We have not sent a messenger except in the language of his people to clarify ΛΉthe messageΛΊ for them. Then
Allah leaves whoever He
wills to stray and
guides whoever He
wills. And He is the Almighty, All-Wise.
I could go on and on but you get the point, as I was finishing the Quran theses verses kept being reiterated and for a statement to be emphasized to this magnitude the message is clear as day. May Allah open our hearts and will for us to be guided, for guidance is only from him Allahu'Akbar.