What is the dosage of folic acid?

My 2 year old daughter was prescribed 2.5 mg folic acid for 3 months in the U,K. She only weighs about 13 kg and has not been eating for a while with very little appetite. I was under the impression the max dose is up to 1 mg/ day but I have seen regular doses of 5 mg / day. Any input would be helpful.