I've had good results with RetroClean. I've just used it with hot water.

I've had amazing results with 1/2 Biz and 1/2 cup Cascade in 2gallons hot tap water and letting it soak for 48 hours. That's a stronger solution tho so may not be best for a fragile quilt. But if it's a last ditch effort, maybe. It works great on stained baby clothes.

I had some fabric that got mildewed and I use borax to soak it in for about 8 - 12 hours. Then rinse thoroughly and hang out in the sunlight to dry. No stain on most of it and no odor. I have also used retro clean but this was cheaper.

Thank you all for your advice!