Could you go and get some sample of the mushroom and find out if they are poisonous to dogs? It does sound suspicious that it would be the mushrooms but the food could have been contaminated. I would have that tested as well!
The mushroom thing worries me about my dog too because she is a vacuum cleaner and will scarf up everything. We’ll be walking down the street and suddenly she will stop and eat something on the road before I can even know what’s happening. UGH! It will already be gone before I look so I don’t know what she’s even eaten.
Sorry for your losses! So sad!
