Ah Holly, I want to come over and give you a big hug!
I can't begin to imagine how you feel, but I do know that your mom lives on in you, in Bubba, and all the things she taught you that you will teach to him. Mom wouldn't want you to give up, she wants you to live on and continue her legacy through Bubba and his children and grandchildren.
The pain you feel now will subside, but you do need to grieve, you do need to get mad. There is NOTHING you should feel guilty about. You did everything you could for mom, and more.
My grandmother died almost 15 years ago now. She was in Florida, my mom was here in Massachusetts, and she tried to get there, but before she even left, Nammie passed away. My mother felt so bad that she wasn't there for her, I believe that Nammie didn't want my mom to see her like that, that she went when she did because she wanted my mom to remember her as she was, not as she became. Your mom didn't want to leave you, but she also didn't want you to see her suffer any more than she already had.
Please, please, please lean on us...we're here for you. And, please call your doctor. There is no shame in asking for help, or asking for something to get you through the next few weeks. It's not supposed to be easy, but they can make it a little more bearable.
Try to take a little time for yourself, go for a walk around the block, talk to mom about the gorgeous weather, the feel of the sun on your face, I'm sure she's listening. She'll show you that, maybe not as soon as you want, or in a way you expect, but she will.
I'm coming over on Thursday, or meeting you somewhere, you just tell me where and when.