It's difficult to comment with advice on separation issues when you have no idea of her background. It seems to me that something has happened to her in a house when she was alone in the past as you say Loki is quite content to stay in a vehicle.
Having the other dog (very handsome) may help but you are wise to check that out first - the worst scenario - you could have 2 dogs screaming! Sorry to be flippant.
I would agree with Moth about the possible need for a behaviorist.
Welcome to the forum to you, Loki and possibly A N other.