Thanks feastathome for your reply...
I had 2 quarts of gravy made from roasted turkey and veggies that were simmered in broth. After solids were removed and gravy was cooled, I skimmed off the fat into a saucepan and added 1 C. flour to make a roux. When that didn't thicken the gravy. I repeated the above.

I now have about 1 qt. of gravy, after trying to reduce as a way to thicken, which also didn't work. Scratching my head as to why this gravy won't thicken! Should I add rice flour? I read where that would thicken gravies quickly. I'm also concerned I need to make more gravy at this point as 1 qt. may not be enough for 14 guests.

My go to fix is cornstarch - a bit at a time and whisk the heck out of it. I'm perplexed too.

You may also try a cold roux with same ratio of butter and either flour or cornstarch, mixed thoroughly. If you do have more stock, reduce some separately, and add afterwards.

Thanks BakerRB - perhaps I'll try the tapioca on the side and add to the mix if successful. A friend had also suggested that.

Derrick's suggestion has worked for me. If you have to , buy a store bought jar and mix it in with your homemade gravy, no one will know but you and me.

Thanks Derrick!

I'm on the fence between using tapioca starch flour or cornstarch. Are they interchangeable, do you know?

Thanks for the tip Leith!

I had read about that as well - perhaps another trip to the store is in order! :)