Since you say the blocks are generous, make sure you try whatever stabilizer you decide to go with on a sliver of fabric/ or the extreme edge of the block. Maybe she had some extra fabric??
You can use stabilizer on poly and silk. Just need the right one & pay attention to iron temp.

I agree, use a fusible lightweight made specifically for silk or very very lightweight product.

Use a lightweight fusible interfacing to get the fraying under control and make cutting much easier. I've made a few silk projects, stabilizer is truly a must, and really works well.

You don't say what quality the silk is, but considering it will be a wall hanging why not use a beautiful silk for the background and piecing. Jenny and Simon Haskins often use it for their embroidered/or not, quilts, backed by fusible pelon, and they are gorgeous. You can see some on her website.

I recommend a woven interfacing for stabilizer. That is best for stabilizing t shirts for t shirt quilts. Good luck.

Absolutely stabilize before doing anything. Then you have a variety of ways to go. You could sash everything to get uniform shapes and sizes or you could do more of a modern look with having them randomly placed on a background. This would depend on the art and the type of folks bidding on it. Be sure and take lots of pictures for her, yourself and (I'm sure if you asked her and her parents they wouldn't mind) us to see the finished work of art.

My first instinct is to sew the silk blocks to a light preshrunk cotton and stay stitch around the blocks before doing anything else.

I agree with the stabilizer! Your life will be much easier after using that. Adding sashing to make the pieces all the same size is a good way to go, but might be hard with the circle. It can be done tho. I am thinking batiks might be good for your sashings, perhaps in tonals rather than bright prints. You can also applique' the circle to it's backing square rather than trying to set it into the background.

I'm not a Pellon fan but that might be okay. I used Touch of Gold fusible interfacing when I was sewing on silks. It works great. I'd watch taking advice from and retail site. They will naturally steer you to what they sell which may or may not be the best alternative.

Fuse for sure. will make it easier for you to work with and the total project look good. Enjoy the journey!!