@feruze-- She could have gotten it from another baby, or even from you.
Sometimes people can carry the MRSA virus in their system without any apparent symptoms. Since babies have weak immune systems, the virus can cause infections more easily in them.
You might want to get tested for MRSA as parents to see if you passed the virus to your daughter. If you also have it, you should get treated so that you don't pass it to her again and again. If it's not you, then there is little point in trying to find the cause. Just make sure she gets her MRSA infection treatment and keep her away from other kids until the infection is gone.