I said something horrible about my mom and I feel really guilty, HELP?

My mother is going threw a really hard season of her life, she did somethings that were really hurtful to our whole family and the things she did significantly hurt every aspect of our family. It was really hard watching her do these selfish things and not have a shred of remorse for them. Anyways now everything is really catching up with her and its been two years. My family has always tried to be supportive and loving towards her because we knew someday things would catch up to her and they have and we wanted to be there for her when she was ready but there is a lot of hurt and anger there and she now she is just so depressed she cries so easily and so often she always looks like she is on the brink of tears and she gets mad at the drop of a hat. But I love her so much and I want her to be happy. Anyways my sister called me today very angry because my mother and her were fighting and my mom said so really bad things, things that should not be said to anyone ever much less from a mother to daughter, so my sister was very angry and I said that I no longer felt like my mother was a good mother, she used to be the best but now she has to much going on to really be the kind of mother I am sure she wants to be. And I said that if my husband and I were to die, I would not feel comfortable with my parents raising my son. UGH i can not believe I said that!!! I wanted to kick myself for saying that. WHO SAYS THAT KIND OF THING! Why did I say it???? I feel so guilty, I cant even sleep. Please help me to get over the guilt of what I said. I so hope that what I said NEVER makes it to my moms ears that would hurt her more than she is already hurting. I feel like the worse person in the world right now, my mom is in shambles and here I am acting like she is not good enough to raise my son? She raised me so who am I to say she wouldn't be good at raising my son. I am just sick about what I said. Please help.