Magistrates in Plymouth, England, heard Ann Duffy, 50, called the Plymouth Register Office Nov. 5 and claimed to be her now sister-in-law to cancel the scheduled Nov. 25 wedding, the Plymouth Herald reported Friday.
The court heard Duffy then called her brother and told him to put her on speakerphone so his fiancee could hear.
"You better put this on speakerphone. I have saved you on the divorce," she told him. "I have canceled your wedding. Would you like me to send you the confirmation email?"
Duffy's brother was able to rebook the wedding the following day.
The court heard Duffy told authorities her relationship with her sister-in-law became strained when Duffy's mother moved in with the couple. Duffy told investigators she did not want her brother to marry someone she dislikes and who she believed to be taking her mother away.
Police said there were other reported incidents of trouble between Duffy and her sister-in-law that led to the harassment charge being filed.
Duffy is scheduled to be sentenced Feb. 11.