divorced parents, one hates the other

How do you deal with this? My parents got divorced when I was 2, so I've never known them together. My mom always hated my dad. I can understand why, but 19 years later she's still bitter over it. He's apologized again and again for what he's done, and he became a born again Christian so he's not the man he use to be. She's always took our time away together, tried almost everything so I couldn't see him, and she always just has something bad to say about him to me. And I'm very close with him, he's always been an amazing dad to me. No matter what age she'd say stuff about him to me, just mean things. I once stood up and told her to stop because he's my dad and I love him. She did for a while but eventually she'd do it again. Even recently, I'm currently pregnant with my first and I we were discussing day care I said it'd help if my dad moved back(he's been thinking about it)because my stepmom would babysit and she says "you'd let her watch him?" Like seriously? I told her yeah why wouldn't I? She just gave me a dirty look. Whatever I ignored it. Well now I'm going to be leaving in a few days to visit him because he got spring training tickets for my birthday and I only see him once a year and it's going to be my 21st. I asked her last week if she could possibly take me to the airport if my boyfriend can't she said it was fine. But I brought it up again today and she now can't because they're going to church that night for Ash Wednesday.. I mean I get that's something maybe important to her, but I had already asked her and I know(been dealing with this all my life so I know) she's only doing it so I might not have a way to get there because I'm going to see my dad. I'm just so frustrated with her that she still does this, especially now that I'm going to have a child. Because if she gets mad at me for something stupid like anything to do with my dad, she'll do something like not watch him or whatever(just an example). I just don't know how to deal with this and I don't want my child to ask about this type of stuff and wonder why his grandparents just can't get along when they don't even deal with each other anymore. Again I do see where my mom is coming from, he's told me what he did to her and put her through and I know there's probably more he won't ever tell me, so I'd probably feel the same way she does but it's just been almost 20 years I wish she'd just let it go or at least not say bad stuff to me about him... I mean it's taught me if things don't work out with my SO for some reason I'm not going to do that to my kid because it's still their dad.. ugh sorry just venting and just wish she'd stop doing this.