I am so sorry to hear that.
I had to look up the Mountain Feist breed, they look like fun dogs and I’m glad you were able to save them.
If I may ask, did you contact the NexGard company, and, if so, what was their reply?
She said last night when I talked to her that they have never seen a bad reaction from the real Seresto collars but see plenty from the counterfeits. Mine will never take another monthly flea & tick chewable. Like she said, if the collar causes a reaction like a rash, etc. you just take it off. She said to let everybody know that Seresto has a statement on their website to let you know how to tell real from fake. They are even being sold in some of the retail pet shops that should know better. I read it and a terrible odor is one clue. The tin packaging is another clue. She also mentioned the price. A lot of the counterfeit collars are selling "on sale" for half what the real collars cost. Mine were $60 each at the Vet and they don't mark them up. They have five Vets and the clinic has it's own store inside the building and online so their prices are reasonable.
This is my Abby. She was in and out of the hospital for two weeks after the Nexgard reaction.
This is all three together. Amy is on the left, Abby is in the middle, and Jack is on the right.
All three are house dogs but they have a big fenced yard attached to the end of the house. I was smart enough to put up a 5' fence. LOL