I am so sorry you are going through this. I know all too well what it's like to have a cavalier that loves fabric. This thread has brought back memories because I had a cavalier that was not as fortunate. I am telling you this to keep it in mind and not to upset you. My girl Ella was at my parent's beach house one weekend and long story short she had an obstruction. It took some time to find out what it was because it did not show up on an x-ray. I re-read the thread today to remember but they had to do surgery and found a string wrapped around her intestines. Don't know where the string came from. They had to remove 70% of her intestine. I put her to sleep because of several reasons including she had very severe SM but it would have been hard for a healthy dog. Ella was 5 years old and never grew out of the fabric eating. Unfortunately, we had been to the vet before because of an obstruction.
I found some articles and don't know how good they are but wanted to share. I know you are watching and doing everything you can but obstructions can get serious and you may want to know warning signs if you have a habitual chewer of fabric. I would talk to your vet and see if he/she has any ideas mainly.
Please know that I have been thinking of you.