Fancy- it sounds like there are issues there that are not related to distance. Maybe your DIL is relying on her own mother more since she became a mom herself and maybe (however unintentionally) she does not feel comfortable being a mom around you? I know my own children have a much closer relationship with my mother than with my MIL- I think that is the way with lots of families- my brother's kids are not close to our mother either- much more to their other grandparents.
Your DIL has to feel welcome as well-did they visit before they had your DGD? Have you ever fallen out, or did you just drift apart somehow? 1.5 hours is nothing really- no excuse not to visit if they really made it a priority.
Sorry you are hurting over this, but do try to work it out.