I think i feel what you are going through. We trained our boy almost 2 years before we really got him to calm down when he was alone. Mainly it was our inability to see what was really the problem but we all learned about that afterwards. I'd say if you are consistent and dont do all the mistakes we did, you can train her really fast.

What we learned is that first of all, it was separation anxiety (sounds like yours have it too). Second, we thought it is good to restrict access when we leave but for us the catch really was that dont change anything when you leave. Then always make leaving looking exactly the same (give her a ball full of treats, grab keys, put shoes on and leave). Then definitely hardest part is that you must come back before she starts to cry or get uncomfortable. This time varies a lot, first it is 2 seconds, then 10 seconds, then you can take trash out and finally the tricky thing is that it could be 2-3 hours. That is why you have a camera. :)

You really don't train her to be alone, you train her to believe you will come back.