She wasn't happy yesterday,I think.

She wasn't happy yesterday,I think.
要把这个句子连成一句的话,应该是：I didn't think she was happy yesterday还是I don't think she was happy yesterday?
有谁知道的,急
哪位高手可以说的明白一点,这个涉及到否定转移,也涉及到时态的问题。