Eric Dargan

Matthews Grip makes 40x40'' steel frames for less than $50 that will fit in your car and you can skin with whatever you'd like. You may need to make your own fabrics or have them made since it's an unconventional size. https://www.bhphotovideo.com/c/product/144511-REG/Matthews_539190_40x40_Cutter_Frame.html

Another thing to keep in mind if you can, is the time of day to position the sun so that you don't need to have it in frame. Obviously, the sun will be a huge specular highlight, but also any buildings or clouds that are blocking the sun will have a bright rim that will push your camera's dynamic range. If you can shoot with the sun at closer to a 45 degree angle from the camera, it should clear the frame and still give plenty of contrast to the landscape. Time of day is huge when shooting with the sun.

@Jon O'Brien, Provided you were hired to document this performance and got there before it started, it may be worth carrying some in-line dimmers in your kit for situations like this. Oftentimes lamps/bulbs are bought without thought to the output and more the aesthetic style. I'm sure since the room was filled with daylight she would have still been able to see her music just as easily. Carrying a few in-line dimmers would give you a bit more flexibility on any jobs you have in the future. Cheers