Thats terrible! why is she doing this, if you are in US and she is too, and if you have the admittance from her that she did this indeed you can hire a lawyer to send her a letter to stop her and threaten to sue for reputation damages and business loss, I have a lot of friends lawyers in US, Europe and other countries since I connected with them at my previous job, I get tons of freebies from them and one time I had a such thing but not for IG, with one letter the threatening and one call from one high profile lawyer I know the person stopped, backed out and is still paying me for the damages he did, we had him pay even it was at that time a short lived damage, he didn't have money so he is on monthly payment plan. You need to show this person the RED EYE now, no one should ever do such thing no matter how much he/she hates you, period. She or he needs to move on. Every person should respect other and be professional, no matter where is the person is, US, India, Middle East, Europe ... never let them take an advantage or do a damage. As a matter of fact you teach them a lesson, RESPECT is very important, hate is very bad, many people do it on the heat of things, they may not be bad people thats why the lawyers can be an advantage because for me that person meant to damage my reputation and let me look bad, he was not a bad person but he was on the heat of the moment and acted when he saw what the lawyer did he learned a lesson and stopped and may be turned his life around.
Go no and do something about it, this is terrible.