Dog Training for unusual personality?

I'm having trouble dealing with my new dogs personality. I choose min pins cuz they're upbeat, i've trained two before. But this dog almost seems like if she were a human she'd be on antidepressants or something. How do I deal with such a humble, sensitive & easy to upset dog when teaching commands & discipline? she's about 2-3yrs old, maybe she was spanked or disciplined in a counter productive manner before, cuz she's really a smart dog, she's catching on quickly but i'm just having the hardest time keeping her from being upset