breast milk vs. cows milk after first year.

My 12 month old still nurses about 4 times a day. She eats some solids but still only has 2 teeth so it's not much. I tried introducing cows milk but she hates it. What's the difference of keeping her on my milk vs cows milk? Does she ever need cows milk if she gets breast milk? I know cows milk has a lot of nutrients too. is breast milk better after the first year or is cows milk better after the first year? Obviously I can't force cows milk onto her but I'm getting stressed out thinking she might not be getting all the fats and calcium etc..she may need. I been reading breast milk is not an alternative to cows milk. I'm so confused . What did you mommies who exclusively breastfed do? Need input ,thanks!