Try taking a completely different tack.
Talk to MIL about how she found out information about what to do with her babies when they were born - feeding, sleeping, nappies, baths, etc etc - everything.
Hopefully she will love having the chance to show off everything she did and remembers... Then - you can attack get to work and convert her 
Depends slightly on what she says but hopefully she will say that she found out up to date information, wanted the best for her children and so on. In which case you can show that you are doing all the same things she did - finding out what are the best practices currently. Try to be nice about it - make a joke about how things move on all the time, that things change even between having dc1 and dc2 (assuming no twins!) and apply passive aggressive pressure isn't it nice that you both have the same way of doing things (ie the finding out best things to do) and it's so nice that she wants the best for her grandchild and isn't stuck in the past.
On the other hand, if she did what her MIL says
point out that research moves on - best example is fall in cot deaths just by changing advice to put babies to sleep on their side - and then a further fall by changing advice to put babies to sleep on their backs, and that by trying to make you do what she did - which is actually what dh's grandmother did, she is asking you to ignore the wealth of research from the last 40/50/60/etc years and if she doesn't love her grandchild enough to want the best and most up to date information to be used to inform you in looking after her grandchild, then she is not really fit to be a grandmother, because what sort of granny doesn't want the best for their child but is happy for them to be brought up according to old outdated thoughts that are known to carry much higher risks to the child's health and indeed life...
And so on -take what she said and twist it round so that either you are doing the same thing she did (even if what you are actually doing is completely different) because you want the best for your child. Or tell her that if she doesn't want the best for your child then she obviously isn't a very good granny, or some combination of the two approaches depending on what she did and you've got a chance of getting to her.
If it doesn't work, find out who she doesn't like and point out how her approach is just like the way that [person not liked] goes about things, that you never had her pegged as being the same but you can see that she is...
good luck!