Even if her season is due, she won't be at the fertile stage in four days. As Susan says, if she is not in heat she will not be at risk. I have entire dogs and bitches, the bitches only come into season every six months or so despite being around the entire males.
When was her last season? If her next one is due I would ask your friend to be extra vigilant, but a bitch in season is of minimal interest to a dog until she ovulates and is at the fertile part of her cycle. This is about a week after the beginning of the season.