Honestly, Widow should just be reworked. The mechanic and sole concept of a hitscan instankill with no damage falloff where the only limit to kill is line of sight is just unhealthy and will always be oppressive to play against. Some ideas I have in mind would be :

Turn widow into a flanker sniper instead of a normal backline sniper, probably with more mobility to contrast her from hanzo and Ashe. She already has the grappling hook and utilizing it to upgrade her mobilty at the cost of the raw strength of her scope shots could balance her out and make her gameplay more in line with what Overwatch heroes are designed to work with.

Turn widow in a supportive dps like Sombra is. Having lower outputs of damage in exchange for more utility that helps the team. She already has her ultimate which works in this way technically, but with current widow her ult is more of a buff to herself than actual information for the team. Another way to help with that route could be to change venom mine to make it more like the animated short version: maybe it could create a cloud of poison that damages those inside, effectively enabling widow to create space for a dive and turning her value away from literary nothing but insta kills.