How do you comfort your mother?

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Yesterday night i went to church for the Ash Wednesday Mass, as i reach our house i ask my bro if mum is still at the house or gone off to hospital to visit my sick grandmother, my brother said she alredy left. then after a couple of hours my mum called and she was crying. She is crying not because of my sick grandma but because before she left the house she had a talk with my sister, unconsiously my sister hurt my mum's emotions. My mum wants to talk to me but since i was in the church she left the house early and called me instead. honestly, i didnt handle the situation perfectly. i dont know how to comfort my mum amd what to console her all i can do is listen to her and tell her that my sister didnt mean that. i told her to talk to my sister to clear the issue but she refused because it may cause bigger problem she said she just want someone to talk to and let her voice out her emotional pain. i hurts me so bad hearing my mother crying over the phone and im there helpless and cant do anything even hug her. on that moment i think i comfort my mother even for a bit just by listening to her. how do you handle this kind of situation? do you sometimes feel lost too and dont know how to help your mum?