This is sticky situation, but one that is possible to handle with a little tact and finesse. A good start is to thank granny for all her expert help and advice (she raised you, after all and you turned out well). Then you can explain to her how important it is to you, to test fly your new mum wings and gently remind her that the best way to learn is by doing it for yourself.
If the gentle reasoning doesn't work, you can try to be a little more forceful without pushing her away. Attribute your baby care information to your paediatrician. So the next time your mum says, “well, when you were a baby...” you may respond with “my doctor says that...”
Do try to keep in mind that all new mums can really use the help. Learn to set up some boundaries, but don't close the border to granny, she's an important part of your baby's life.
