I thought that the Queen made everyone believe later on, like when the guards tried to kill her in Snow Falls, that by that time everyone believed that Snow had done something like treason and murder like it said on the wanted posters. It may be that the Queen tries to frame Snow for Snow’s father’s murder so then all the guards are no longer loyal to Snow, but later on it comes out that the Queen actually did the murder and that is when the Queen loses their loyalty.
It may be at the time that the huntsman is sent most of the guards are still loyal to Snow though i think that there were some guards in the room when the Queen was talking about sending the huntsman. It is sort of unclear. Maybe a few of the guards are loyal to the Queen. Maybe she has a few of their hearts. I don’t know.