Also, do remember that Interpol would have been in a position to contact her immediately and possibly advised her to take that action.
I don't think Interpol is in the business of advising people with direct links to mass shooters to delete / destroy possible evidence. Ditto for those with direct links to say, suicide bombers.
I agree, there are many plausible explanations as to why she deleted the Facebook account at that time. These explanations include grief over an ended relationship. Another plausible explanation is that she knew or strongly suspected the attack was going to occur and was waiting for news of it.We have no information that he reassured her by telephone of her fears or that they had any subsequent contact at all.
If she was grieving it is possible she deleted her facebook a/c for that reason, she possibly did not want contact with others for a time.