The issue with Warlock is there are no healing spells. What we really need a is a cleric and if she had a 13 wisdom she would multiclass into War Domain. Divine Soul is the next best thing for someone without a decent Wisdom.
What we really need healing word and spare the dying. A few other spells like Protection from good and evil and shield would be nice too of course.
The DM has a house rule regarding stabilizing PCs, if you fail your medicine check that counts as a failed death save, so it is pretty nerve racking trying to help downed PCs. Healing word or spare the dying would fix that.