Dear querist,
The burden of proof lies on shoulders of that person who has given letter to you stating such things.It's better to give proof first as he wants to cancel the marriage.
The moot intention of the informant here is to cancel the future marriage.As he may be her ex or somebody who wanted to marry her.Better talk to him as why you have given me letter and what is te interim intention in doing this.
There is no any data base maintained. But yes if you are so keen then visit to her parents house court jurisdiction and seek information regarding her in family and session court as any civil or criminal cases in past was there or not on her name.Even you can take help of Police to find out the details.
Thanks & regards,