um, i would keep breastfeeding him if thats working for you both. Why on earth would she think that cows milk or toddler formula would be better for him than your breastmilk which is made for humans?!?
My ds was still breasrfed at 12 months but was having cows milk at daycare 2 x days per week as i couldnt (and couldnt be bothered either) express enough.
It just my opinion but i think she is wrong. I had so many issues with the MCHN nurse in my area that i only went twice and didnt bother going back, i would suggest you follow your mummies instincts