When around the rear of a horse you should either be out of the kick zone or so close as to make it difficult or less painful if they do try to kick. If its a horse I'm unsure of I stand right at the hip close enough that my arm is in contact with the flank. I keep contact with them all the time I'm brushing so the don't forget I'm there.
If its just Vida I still stand at the flank but don't worry about her kicking. Most horses like having their tail brushed so don't fret too much
I Start at the top and brush from the outside to the middle. Then go to the end and brush from the bottom to the top. I usually hold the long tail hairs in one hand and brush against my leg, turning the tail hair as I go. I like to start at the top so she gets a good butt scratching in before I go to the long hairs where all the snarles are usually at.