Ellen (Season 4)

Location Unknown
Nothing is known about Ellen's life prior to or as the outbreak began. It's possible she had prior prep do to the fact she taught survival courses.

Just in Case
Ellen is found by Naimo as am infected in a landrover.

killed by

 * infected - Ellen at some point was bitten when the building she was staying at was over run.

After finding the complex overrun Naomi found Ellen in the landrover as a walker and stabbed her in the thus putting her down.
 * Naimo (indirectly caused, Alive and undead) - Due to Naomi leaving her sick daughter. Rose, behind while sick she turned and soon infected the whole group of survivors along with Ellen.

Season 4

 * Just in Case