When she's in heat there will be a slight smell and a small amount of discharge.
If however the smell is absolutely foul smelling and the discharge is staining the fur I suggest a trip to the vet. Put a finger on each side of her vulva and push gently, if you get a lot of pus looking stuff coming out, that is a sign of infection and needs to be seen by a vet right away.
If its just a slight smell though and the discharge is minimal then it should be fine
