Venting can help but its only a short term solution to a long term problem.
You really do need to heed the counsel already given.
Some grandparents really shouldn?t be allowed access to their grandchildren.
A percentage of the general population is dysfunctional and/or abusive. That percentage, like everyone else, has children. Then those children grow and have children of their own. The not-so-loving grandparents expect to have a relationship with their grandchildren. The only problem is, they?re not good grandparents.
Many adult children of toxic parents feel torn between their parents? (and society?s) expectation that grandparents will have access to their grandkids, and their own unfortunate first hand knowledge that their parents are emotionally/physically/sexually abusive, or just plain too difficult to have any kind of healthy relationship with.
The children?s parents may allow the grandparents to begin a relationship with their children, hoping that things will be different this time, that their parents have really changed, and that their children will be emotionally and physically safer than they themselves were.
Unfortunately, this is rarely the case, because most abusive people have mental disorders of one kind or another, and many of these disorders are lifelong and not highly treatable. (Others are lifelong and treatable; however, many people never seek the necessary help.)
The well-intentioned parent ends up feeling mortified for having done more harm than good by hoping things would somehow be different ? instead of having a child who simply never knew their grandparents and who was never mistreated, they have an abused child who is now also being torn apart by the grief involved in having to sever a lifelong relationship with the unhealthy people they are very attached to.
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More Here: lightshouse.org/lights-blog/toxic-bad-abusive-grandparents#ixzz2cS0FkwVz
I can only reiterate the above and what the other respondents have stated; if she is too toxic for you to deal with, she is too toxic for your vulnerable child.
She will keep disregarding and ignoring any boundaries you care to set. The way forward with such people is to basically cut them off, she is bringing nothing positive into your life but instead creates more anxiety. She will do the same to your DD as she has done to you, toxic crap like this filters down the generations. DO not let your DD have this legacy.
You can reclaim your life back, you do not need her approval any more not that she'd freely give it anyway. It is not your fault she is like this, her own birth family did that lot of damage to her.
There must be someone else willing to babysit; anyone else is better than your toxic mother doing that role. She will poison her against you as her mother.