How about putting a very fine tulle on top of those blocks and/or doing free motion quilting on top of the tulle in the areas around the lettering using an invisible top thread? This should stabilize those blocks. The tulle will be barely visible but would protect the blocks.

Another thought if the fraying is just in the seams....use fabric glue along the seam to stabilize the frayed section and then do some couching with a coordinating cord or yarn to outline the blocks. It would cover the frayed section and also the area that is stiff from the fabric glue.

Since it is tied, I would untie it and take part of one side apart, turn it inside out and go to work fixing it. Very pretty quilt though. Glenda

What a heart breaker! All the work, wish I could help.

I may be just a little looney, but did I understand you to say you washed it before adding the bat and backing? Just curious

maybe outline the squares with ribbon to cover the fraying and provide something to anchor the fabric too? you could use stitch witchery to iron it on and hand stitch it down.