I thought that perhaps I could alleviate some of your hurt by relaying our similar experience. Although I cannot offer you an explanation as to why this is happening, I can attest to the fact that you are not alone.
Our six year old son has, since about age four, become aloof to my in-laws. He was the first, and only Grandchild to these folks for 3 years. They have always been very good to him, and they are very kind, affectionate and generous people. I have always had a good relationship with my in-laws, and my husband is very close to his parents as well. Until recently, they lived only a short distance from us, so we (husband, son and I) saw them quite frequently - several times per week. They currently live 30 minutes or so from us...just far enough that we only see them on weekends. In any event, at about age 4, our son decided that he didn't want to be affectionate with my in-laws, and his attitude progressed to where he doesn't want to spend the night with them, and could really care less about seeing them. This attitude and behavior perplexes us, and has hurt my in-laws (mother-in-law especially) very deeply. We are 100% certain that our son has not been mistreated in any way while in their care.
Alternatively, our son is very excited to see, and very affectionate toward my parents who live hundreds of miles away - so we only see them a few times per year.
There are only a handful of explanations my husband and I have been able to come up with - all of which are pretty lame to us. First, my in-laws are not willing/able to do much physically with our son (who happens to be a very physically active boy). They are very interested in him and attend his activities, but their physical interaction with him is very limited. Additionally, we've thought that maybe he got too used to seeing them regularly - sort of the opposite of absence makes the heart grow fonder. Lastly, his Grandpa can be very stern with him when he misbehaves, however, he is also very affectionate and loving toward him at all other times. Like I said, these seem like pretty lame explanations to us.
We have tried to strike a balance between his need to be treated more grown up, and respecting his wishes for personal space - and our family desire to be affectionate toward one-another. We do insist that he greet, and say goodbye to his grandparents with a hug and a kiss. In our families, those are issues of affection and respect for elders. I know my in-laws are still hurt - and they continue to try to foster a relationship with him. I hope that some day he will warm back up to them.
Just hang in there for your grandchild's sake. It sounds like you and your husband are a much needed link to family, love and affection for this child. Please don't let your hurt feelings stand in the way of your relationship - someday (hopefully sooner rather than later) your grandchild will come around and appreciate you and your efforts.
It's pretty clear that the inadequate nature of the attachment between your granddaughter and her mother is having an influence on other relationships. This is true of all children, but what is hoped is that the bonds between child and parents are strong enough that they set the stage for other strong,stable relationships. It's understandable that, with the 'fuss' that occurred around recent developments, your granddaughter would have somewhat of a negative reaction. That's quite typical for young children. They react against the adults whom they perceive to be the 'source' of the recent problem. It would make sense not to force the interaction between you and your husband and her right now. Allow a little break, then resume (if that is what her parents and you wish). There's no point exacerbating the strain by pressing the contact now. Be sure to keep in touch, though, simply by dropping over and spending a few benign minutes. Let the dust settle, and things will be fine.