As long as you have another Rebel in this arena, Mon Mothma gets Stealth.
One of your unique Rebels gets Fortitude and Inspiration until it is discarded.
Keywords
Fortitude
Fortitude: An isolated, static ability that means, "This unit can prevent unpreventable damage to itself." Units with Fortitude can prevent damage from units with Ferocity and "damage... that can't be prevented" by using Deflect, Evade, Parry, and other damage prevention abilities. Fortitude only allows a unit to prevent unpreventable damage to itself, not to other units. Putting damage counters directly on a unit is not the same thing as doing damage, and also can't be stopped by Fortitude.
Inspiration
Inspiration: An isolated, static ability that means, "Each of your other units in this arena gets +10 speed, +1 power, and +1 health."
Stealth
Stealth: An isolated, static ability that means, "This unit can't be attacked unless it's tapped or has damage counters on it." An untapped and undamaged unit with Stealth can still be affected by alternative types of damage. (Such as Overkill.) As long as the unit has any number of damage counters on it, it can't use Stealth.