I'm not going to tell my mom that my grandfather passed away because I knew she wanted some of the estate
How can you be so sure that she wanted some of the estate?
I know one thing she is greedy and she won't stop talking about it
It is not good that she kept talking about his real estate before he died but it is not good not to tell her. You should let somebody know when somebody in their family died and she might need to know for legal reasons.
She never cared to know me anyway.
You should still be the bigger person and let her know about the important information, because it would be a terrible thing to withhold. It sounds like this was important to her, and by not telling her, you're being just as bad as you claim she has always been to you.