In shock and not sure what to do!

I am 52 years old. My brother, myself and my mother all had our DNA tested on 23andme as of a year ago. Yesterday, I received an email from 23andme saying that I have new DNA relatives, which happens fairly often. Usually, it is a 3rd 4th 5th or more cousin. This one came up as a first cousin. I have access to my mothers log in on 23andme as she does not go online too often except on her cell phone so she agreed I can just log in for her and let her know any updates. I checked my page and saw a woman who they predict as my first cousin. I logged into my mother's page and it said they predict that this is her granddaughter and that she asked to share DNA. I believe I have found out that I have a sibling I never knew about and this person contacting my mother is my niece. She sent a message to my mom letting her know that her mother (my sibling) passed this last November. The way she said it was almost, but not quite, like she has already been in touch with her. I do not know if I should let my m know what I have found out. I do not know what the right thing to do is. I am so sad I lost a sibling just 2 months ago that I never knew and so sad for my mom for what she must have gone through. Please help! Thanks

The only thing you can do is to tell the truth. This isn't just her daughter and granddaughter.This is your sister and your niece. You can contact your niece yourself regardless of how you handle your mother. - Adult Adoptee

That’s always just one of the fears to find one party has deceased. But in your case she has a grand baby. A little piece of her daughter. You should let her know. She submitted the test knowing its for better or worse. I’m so sorry for your lose. Waiting for her mom to of passed makes me wonder if her mom wanted to know or if just the grandchild does. My husband (the adoptee) never had kids. It’s better to inform your mom no matter the result.