Change of Sponsors (J1)

What happens is that I'm having trouble with my sponsor and I would like some advice. I'm from Argentina and I have been working here for 6 months, been an intern of a Internship program. I work for a company with Sales and Marketing, but what happened was that they told me that I would work directly with Marketing, but the company that I'm at never followed the training plan and I'm not really learning anything. I searched for another internship that agreed to be my sponsor, but to leave I need the signature of my currently sponsor, and she doesn't want to sign the papers. Everything is fine, I have already found a new sponsor and everything will be legal, the only problem is that I can't go if she doesn't sign the papers letting me go. She says that if she lets me go the other interns would maybe ask her for the same thing, and that I signed a contract for 18 months and I'm leaving after 6, but if her internship is not following the training plan and after I have talked to her and nothing changed, all that I can do is leave. What should I do? Is it possible to solve my case without a lawyer or how much would it be to have a lawyer to help me?
Thank you very much for your attention.
Yours faithfully,
Priscilla

If they have failed to follow the agreed plan then they have breached the agreement and you are not bound. But save all evidence in cas it somehow becomes a legal matter.