A.P.
Hi, Christina! :)
I just read your request and for some reason (maybe the Holy Spirit??) felt I should share my 2 cents. ;) I'm 37 and am married and have 3 children, ages 15, 2 and 8 months.
My mother and I always had a strained relationship, so I can empathize w/you on that. She was a great mother, and self-sacrificing to a fault (which wasn't the best example for me or my brothers either),but there was always tension between us (from what I understand, this happens with most mother/daughter relationships anyway). She always had an opinion on everything (from who I was dating, to how I was raising my son) and I was always made to feel guilty if I didn't do things "her way".
But, I have to tell you this. I miss her more than words can express. She died of cancer within 4 months of being diagnosed, at age 56. My heart has been broken for the entire 7 yrs. she's been gone. I never realized just how much she meant to me until it was too late. I'd gladly put up with her stuff, if I could just have her back. I'd put more emphasis on working on our relationship instead of complaining like I did and wishing things were different. I'd see what I could do to make things better on my part. I wish she could have been here for the births of my only daughter who's 2 now and my precious little boy who just turned 8 months, who looks a lot like my mom...
My point is this...please, please do anything you can to save your relationship with your mother. That doesn't mean giving in to "her way". But talk to her lovingly, telling her you value her opinion as your mother, but you are a mother now and it's up to you ultimately to make the right decisions for your children.
As far as the visits go, you could tell your mom you'd love for her to stop by on a planned visit sometime, so she can spend time with your daughter. You're right...it's not "her right" to see her granddaughter, but it's in your daughter's best interest to have a relationship with her. You don't want her to sense a strained relationship, or she will naturally not trust her (may be the reason she cries when she's around her). Children are highly sensitive to parents' emotions. So far, your daughter doesn't know all that you do about your mother. She just knows what she sees in you when she's around. If you see over time that your mother is influencing her in a negative way (like, does she act-out after a visit), then obviously things need to change.
You have every right to refuse your daughter to stay w/your mom and step-dad if you do not feel this is in your little girl's best interest (sounds like the step-grandad is the worst problem there). However, when the visits are at your house, it's on "your turf", so you can control the environment. ;) If your mom can't drop by during the week, what about on the weekends?? You might suggest a Sat. or Sun. afternoon visit, but tell her you have plans that night (even if it's just your own family night at home), so she'll know there's a time limit.
I really hope and pray things can be worked out. Because, I can 100% promise you this. You will miss her terribly once she's gone. I just don't want anyone to go through the coulda-shoulda-woulda that I go through in my mind since my mom has been gone. I wish I could have told her I loved her more (that hardly ever happened). I wish I could tell her how much I appreciated the good things she did for me. Focus on the positive and pray about the negative. The Lord wants you two to have a wonderful relationship and only He can heal the hurts and make it better than you could have imagined. Place it in His hands and watch what happens. :)
Best wishes to you, my dear sister in Christ.
A.