Legend has it that Perseus killed Medusa by getting himself a mirrored shield, and instead of looking at Medusa directly during the fight, he looked at her reflection in the shield.
I have no idea how this worked logistically.
If Perseus held the shield in front of him like most warriors held their shields, he probably wouldn't have been able to see much of the reflection (unless the shield was constructed of some metal that was designed to reflect up, a la black patent leather shoes).
Maybe he had a segmented shield, with various panels at various angles causing a series of reflections that would render Medusa visible. Of course, that shield probably wouldn't do him much good in combat.
The only other option I can think of is that Perseus walked backwards towards Medusa while holding the shield up over his head at an angle, like when you're trying to see the back of your head with a hand mirror and a bathroom mirror, and then when he got real close, he closed his eyes, spun around with his sword drawn, and slashed Medusa in half. This plan would fail spectacularly if Medusa was capable of any sort of fighting apart from her curse powers.
I think the "Medusa saw her own reflection and turned herself to stone" variation of the myth was designed to compensate for that narrative shortcoming.