Shadowverse

No. Medusa doesn't have a clash ability. She just has an ability that triggers when she attacks. Clash is when units exchange attacks, and it doesn't matter whether the clashing unit is attacking or defending.
By the way, I don't like that they made an icon for Drain, for Bane, for Last Words, but they use a generic flag icon for other effects, indicating that they trigger under certain conditions. There are too many abilities with just a generic flag icon. They could have made an interesting icon for Clash, like two crossed swords or something.