Yes, one DGD is a miracle child (I know they are all miracles really), but DL has been told that it would be too dangerous for her to have a second one. As my son and DL were told they couldn't have children in the first place, they were completely stunned when DL was pregnant. DL had a dreadful time though and, having spent a lot of time supporting them during pregnancy, we (DH and I) fully understand why they won't/can't have another. I feel sorry for them, not expecting to have a child, they were completely uninterested in friend's children and have had an enormous shock. They are trying to do everything 'by the (current) book' and it makes for awkward visits now because we don't agree with everything they tell us they think they should be doing to assist her development. We don't want to upset them so find ourselves biting our tongues.
While our DGD is loved and cared for, she is very much in charge at 2 years of age! We don't see much of them now, we may upset DGD's routine that they are trying to establish, may upset her random mealtimes, bathtimes, bedtimes etc. DL's parents seem to be happy to just do as they are told and idolise their only DGD but we are older, have a little less energy and, as in-laws to DGD's mother, are in a different position. If they had been able to have a second child, our DGD would have had to adjust to her parents sharing time with a new baby. I'm not sure that I can cope with the little tyrant that is our DGD. I know it's not her fault.
I thought we were getting on OK with our DS and DL but once our DGD was weaned and became a toddler, we have seen less and less of them. I'm taking the advice I have seen on these forums, just keep the door open and don't rock the boat (to mix a few metaphores)!