Do you have to apply all die results? A situation came up in which we were both left with one player. But she also rolled a result that would have resulted in mutual suicide(the unit ability of cause one damage but remove a unit). Does she have to resolve that result or can she choose to ignore it?

Special abilities from die rolls are up to you to commit or not. If a unit rolls hits, morale or lore results and has no optional choices for any of them they're automatic. That is, you can't roll morale results and choose to ignore them, unless you have a special ability that lets you commit morale results to something other than forcing the unit to retreat.