I am older and have see countless OW try to compete to be MOTY. NEVER once has this worked.
Be glad that she is kind to the kids - beats the alternative.
No matter what she does she will NEVER EVER EVER come close to replacing you in your child's eyes.
A close friend of mine is just not domestic. OW became wifetress when the children were very small. She cooked, she baked, she made homemade costumes, etc - she did backflips. The children are now adults - they tolerate their SM but adore their mother.
Let her compete and compete - she will never win.