Why is it that no matter how much you try to love your MIL, nothing is ever good enough? She is always very distant. How can I bond with her? Any suggestions?

Make her feel important and needed. Ask her all there is to know about her son like his favourite meals, his childhood stories and how to "take care" of him when he is not at his best. I understand the feeling though, trying so hard to get through to people and after years of trying, nothing has improved. But at least I know I've tried and if it remains the same, it remains the same. I won't stop respecting her or caring any less, just that I'm not going to lose sleep over it.