I am so sorry. It's a hard thing to wrap your head around. It's a hard thing for people to talk about in general.
Honor her by being honest, doing the things she couldn't, reaching out. She isn't hurting anymore but her actions have caused so many others to hurt but you knew her to be a good mother, she had to have thought you would all be better without her. It isn't true, but she didn't know that else she wouldn't have done what she did. She couldn't see reality and she didn't show any of you the one hell she was living in inside her. You now have to forgive her. Forgive yourself for not being a mind reader as didn't show you the pain, she didn't, and you have to believe that truth.
Be honest when your hurting. It is a brave and hard thing to do. If others see you doing it, they might be able to and that might save more mothers from the lies that they are alone in this.
Your not alone. I am sorry for your pain.