Some people can't decipher between person and behavior. Your complaint and boundaries are about behavior, and that is specifically, the drinking.
If I understood it correctly, she can not be around your child if she's been drinking, and can not drink around your child. You have EVERY right to set that boundary. That's protecting your child from the pain and anguish you've experienced with an alcoholic parent.
That is -- you're specifically concerned about the behavior. That's NOT judgment.
Judgment is when you insult the person - call them names. Insult who they are.
Very likely, the alcoholic is probably being judgmental. They're complaining behind your back. You probably hear about things she's said through other family members? Through the triangulation? My point is that she isn't deciphering between person and behavior - gets mixed up between the two.
You are clearly outlining the BEHAVIOR that isn't welcome in your child's life. She is arguing that you're judging her as a Person (that's judgment by the way, at least in my opinion).
She's turning it around and saying you're attacking her character. It's all part of the disease. Denial is one of the greatest weapons of the disease of alcoholism.
Stand your ground. Protect your child.
Right now, the only thing that's really bothering you...is guilt. Sibs and your mom are pulling on your guilt string. What are you to feel guilty for? Protecting your child from the inevitable abuse, neglect, etc that comes with a person who's actively engaged in their disease of alcoholism?
Rock on and keep on rocking on. Some studying about your own guilt and why that's plaguing you would be a good direction. Trying to figure out your siblings or your mom won't help you - you don't live in their brains and don't lead their lives. You lead your own. Work on you.
What is it like to grow up with an alcoholic? How has it effected your life? Reading stickies, or literature on adult children of alcoholics can help. Al-Anon or ACOA meetings might help as well.
I'm so sorry your experiences the long, draining, painful experience of watching your loved one slowly killing themselves (some faster than others) with this disease.
Hugs to you and your family (spouse and kid(s)).
(PS - for more perspective on what I'm trying to explain - look up "detachment" -- you can love the alcoholic, but hate the disease - hate the abusive behavior, etc - detach with love - no judgment. The disease is in charge and destroying her life. But you don't have to let it harm you and your family too. -- another thing--> is it judgmental of me to laugh at the "she only drinks after 3 pm"? The fact that in this statement means she's drinking EVERY single day and escapes their logic -- is just part of the insanity I guess - but I totally understand - I once thought I would bring my daughter to visit my dad at work cause he doesn't drink when he's there -- something interesting to consider - an active alcoholic's behavior is impacted by their disease BOTH during drinking BEFORE and AFTER -- my father has said really judgmental and mean things without a drink in his hand -- but in the end? my father is the one making no effort to see my daughter - I feel very sad about it, but I can't fix the disease nor can I control his behavior)