Our first possible heat?

My belgian malinois is just a couple weeks over a year old and she has yet to have her first heat. It is my first time having a female dog so I'm really not sure what all to expect. We currently have a 5 month mal as well and tonight she has started mounting him (she has never done this before). She is also very on edge panting and whining a lot more than normal. I am not sure if these might be signs she that she might be starting soon but she hasn't started swelling or bleeding at all. What were some signs of your girl's first heat and how do you manage a heat? I tried asking my vet what to expect and she was super rude and unhelpful about it, so anything will help!!