HOw do you know when to go to Cows Milk?

Hi Ladies
My DD is 12mths old (well in a week & a bit) & I had been giving her 1 bottle of cows milk + her 3 bottles of formula (Karicare Gold) each day the last week & she seemed all good. So, we upped it to 2 of each. Now it seems she has been blocked up for the last 3 days & barely eating or drinking much. We had a mega chuck this morning about half hour after bottle (she never normally chucks) and then another chuck directly after bottle this afternoon. Since then she's done one hard dry poo + another runny stinky poo.

How do you transition them across? Should I still be mixing or should I reduce the number of bottles per day? I probably should cut her back to thee anyway really.....

Any tips or ideas to help would be appreciated.

Ta.

After my kids turned one, I dropped a scoop of formula from their bottle and made up the difference with cows milk. I would drop a scoop every week, so they would be on cows milk in 4-5 weeks. :)