We''re being sued for an accident that wasn''t our fault. What can I do?

Last year my sister and I were driving to church in our mother''s car, we were about a block from our destination, we were stopped at a red light. I remember that for a fact the light had JUST turned green. When my sister started to turn, a minivan hit our left headlight out, and I know for a fact that she had ran a red light. My sister and the lady pulled over in a parking lot. Meanwhile, I had to run to the nearest house to call my mom because neither my sister or I had our phones. I ran at least a block, when I returned to my sister she was hysterically crying and talking to the police. Keep in mind I was never questioned, I later found out that the lady was questioned first and claimed my sister tried to turn on a red light. My sister, clearly, could not get her thoughts together and they put her at fault. Remember that I know for a fact that the light turned green, and I was never questioned. Now we''re being sued. Is it too late to do something about it? Even if it was last year?