JWs consider a marital engagement as a promise which is equivalent to already being married prior to the legal formality. As she broke-off the engagement, she broke her promise and so committed a sin and will likely have been 'marked' by a few of the elders whether or not she knew it. Some elders will often recall a person's sins, better than an elephant, even decades after a person has been reinstated and is supposedly 'forgiven'.
Since she committed a 'sin' which in itself she could not be disfellowshipped for, the elders were probably looking for anything else they could use as a potential excuse to DF.