Myrna was born and raised in Corel, a small mining town in the western continent. She lived a life of relative peace, marrying Barret Wallace when the pair were quite young.
Although Myrna is never seen within the original version of Final Fantasy VII, she is referenced within the in-game dialogue. From this, we learnt that even though Barret supported Shinra, as he believed the Mako Reactor would bring about great prosperity for Corel, Myrna was against the construction.
It’s revealed that despite the objectives from Myrna over the construction of the Mako Reactor, Barret managed to put forth a compelling argument; this won over Myrna, and also the rest of the town, including his friend Dyne.
Not too long after, however, issues arose around the construction of the Mako Reactor, and they decided to end its construction and cleanse the town.
The initial reason was that Avalanche, an eco-terrorist organisation who were waging war against Shinra, occupied the reactor, and in the fight to reclaim it, Rufus Shinra was “captured” and “held to ransom”. The cleanse was undertaken on the premise that Corel citizens had supported Avalanche.
The secondary reason was that Shinra had identified a more profitable source of energy and wanted to ensure that nobody within the vicinity of Corel could leak this information.
Barret and Dyne tried to fight back against Shinra, but they were powerless. Myrna Wallace was unfortunately killed in the crossfire and it cemented a desire within Barret to make Shinra pay for everything they had done.