How Safe Is Using Oregano Oil For Sinus Infection Caused Post Adenoids Removal?

My 3 year old grandchild has been told to have her adenoids removed. She seems to breathe and eat with her mouth open. She is seeing a homeopath because she easily gets sinus issues which lead to ear issues. If she becomes too cloggy, it appears to make her a little off balance. I was just told at the Health Food Store that oil of oregano might help.