3 main things to consider when playing widow:

1) Is widow a good pick against this team composition? If the enemy is countering you, or is very bulky you should consider switching

2) Am I getting enough kills? Widows primary role is getting kills, she can't reliably contest the point from the back so you need to be killing people before they become a threat to your teammates.

3) Are you communicating with your team? You may kill both of the enemy healers, but if you don't tell your teammates they may miss the opportunity to push. Communication is key, and if you're not communicating you're going to waste a lot of opportunities and teammates won't recognize your effort.

Doesn't excuse these guys behaviour, I wouldn't want to play with them either, but if you never switch in order to give your team an edge, then there's a problem. In a game focused heavily on hero switching and countering you shouldn't play only one hero.