poo smearing

My daughter has been smearing poo since she was 2 and is now 3 and 4 months. The smearing started all over her cot and the walls round the cot and herself. Now that she is in a childs bed it is over everything in the vicinity of her room including her younger brother....I am at a loss now. I have asked many people for ways to manage her behaviour and have tried many different ways to solve it but it still persists...My relationship with the child is now starting to struggle because i have no idea how to deal with the situation..I have my concerns that she has some behavioural problems such as A.D.H.D because she is obviously not right in the head! Any Ideas would be really appreciated.