Thank you so much for the replies. I think I will call tomorrow and see if I can get a second opinion for her. I have tried to search online and can't find anywhere that says the spay is helpful for Demodex. The only thing I can find is where it recommends spaying because you shouldn't breed a dog with Demodex.
Our other Yorkie is so healthy and always has been. We got her from an older couple who bred their Yorkie for the first time and we got to go to their home and met the Mom and Dad and saw the rest of the litter. I tried to find them when we decided to get another Yorkie, but they have moved and I didn't have a phone# for them. Anyways, when we decided to get another Yorkie, we called several places and this lady had a Yorkie "available now" and we went to the lady's house and was strange because she owned 2 houses next door to each other and said one house was for her dogs as a "nursery" and the other house she lived in. She didn't let us meet the Mom because she said she didn't allow people into the nursery for fear the puppies would catch something. I was so naive when she only brought the puppy in to see us and I didn't see the Mom or Dad. She breeds several kinds of dogs (different breeds) and I should have known better (now I do), but I have fallen in love with this dog and my kids are crazy about her. She just fits right in with our family and with our other Yorkie.
Thanks again for the responses. It's nice to hear from others about what to do
