No two children, not even twins have the same childhood. personality is affected by the random selection of genes we inherit from each parent, some times the mix ia toxic and difficult. So do not blame yourself for what your daugher is now.
While I fully unerstand your love for your daughter and grandson, I think sorting this out without risking the relationship will be very difficult.
Tell your daughter that you are getting older and cannot cope with everything. Then give her a timetable of the help you can give. Make it clear that details of the timetable can be changed, baby sitting Wednesday afternoon rather than Thursday evening or similar but the time available is fixed and non-negotiable. You daughter will cut up something rotten, this is the risk of the cut-off, but I doubt it will last long, she needs your help a lot more than you need to give it.
Stay firm despite emotional blackmail and any other threats, until she learns, that you mean what you say and said what you mean. I am sure your son will be on your side.