How do I deal with a non-communucative bridesmaid?

I asked my future sister-in law to be a bridesmaid at my wedding in August last year. I told her upfront how much the dress would cost and could she afford that. My wedding is in September (less than 3 months away now) I had to order her dress in April, she knew she needed the 50% deposit 2 months before then and then didn't have it so I covered the depoist. This was back in April remember, I have tried calling her and messaging her to ask about the deposit and the balance which is due very soon for the past 6 weeks. I have not received any response from her whatsoever. I have also tried messaging her asking about coming up for fittings, still no response. Now my wedding is 3 months away and I have a half paid for dress that none of my friends would fit in to. What do I do?