I think my mum is a alcoholic 😔😞🍷

I'm 18 and me and my mum have always had a great relationship, but ever since my mum found out my 15 year old sister is pregnant I believe she's been abusing alcohol. She has gone through a 1 litre bottle of jack Daniels every two days for the past two months. She has become arguementive, un reasonable and many other things. I've had to learn to just nod my head and walk away. She constantly finds a reason to start a fight out of the smallest situations. I know this is a hard time on her, but doing this is not helping. Is my mum becoming a alcoholic ? Can any help ? How do I talk to her without her exploding ? Help please x