I don't want to reimburse a junior employee who fell for an email scam, it's not my fault
If you didn't reimburse that employee, what would happen to him or her?
He or she will feel bad and probably quit. I don't feel bad about that.
Bad things happen to good people sometimes. I'm sure they have learned a lesson from this and would be more careful next time. I'm sure you can relate to them on some level, as we have all made mistakes in the past that have led to negative consequences.
It's just a few thousands of dollars and he or she still has to learn to be smart.
It's really unfortunate for them and your company to have fallen for such a scam, and it really isn't your responsibility to keep them as they can jeopardize the company. How about trying to get them into internet safety classes first, so they won't learn to do that again?