Thumbwitches, yes a huge step. Even though she let him initiate it, I'm so proud of her and feel genuinely hopeful we (DB, my DH and DD) can get some sort of more healthy, normal relationship with her after this.
Interestingly, my DD's birth was also a factor in the marriage breakdown between my parents (as well as with DMIL, if anyone remembers my previous posts!). My DF was jealous, controlling and manipulative from my pregnancy. My DM was always desperate to be a grandmother and she basically spelled out to him she would be seeing her grandchild whenever she wanted, and he wasn't her priority any more. Cue sulking, aggression and drama from DF.
DM spent 8 months looking after DD for us one day a week, and still sees her every 2/3 weeks and has a fab relationship with her. DF (despite being retired) hasn't seen her since Christmas and simply can't be bothered. When he was still living with mum we were planning a rare visit up to see them and he announced he would be out and seeing his friend (a woman my age who he has spent the last year inserting into any and every family gathering, including a family funeral). We didn't go.
He doesn't even ask to speak to her on the phone. It breaks my heart as DD I think has picked up on the dynamics and is always asking after him. She went through a phase of crying because she missed grandad. 
I have told her we wouldn't be seeing him much as we weren't getting on and he wasn't very well. I don't know how much she understands though, or why she's latching onto someone who has never really spent much time with her, and more or less ignores her when he does.
Do any of you have good tips for explaining to a 3 yo in an age appropriate way why they don't see family members? I'm waiting for her to ask about DH's mum too - although we might get a few years' reprieve there as his dad has remarried, so DD has a step grandmother.