I didn't look before how her counters work, comments in her old flash file made made me believe her melee counter would work the same way as her ranged one.
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Ranged-ranged-ranged isn't viable because her ranged counter action doesn't reset the v1 of the "Counters Ranged" status effect (her melee counter doesn't reset the v1 of "Counters Melee" either, but that doesn't matter since she always counters those). So after the second ranged attack, she counters all ranged attacks (tested it) until you use a melee attack (this means taking damage from her melee counter), because it is the only way to set the v1 value of the "Counters Ranged" status effect below two. And ranged attacks are the only way to damage her. So the only viable strategy, even for melee characters, is ranged-ranged-melee, and her melee counter deals damage.
She counters specials too, so melee debuffs don't work either. For example, a low level merc can't use headbutt to stun her because it's a melee move and she always counters those.
EDIT - I forgot to say that her melee counter sets the v1 value of "Counters Ranged" to 1, not 0, so the actual pattern is ranged-ranged-melee, then ranged-melee-ranged-melee-(etc).
I don't know how much of this is working as intended, but those were the things that made me rise an eyebrow when I looked at the code.