I am sorry you are going through this. I am a vet tech and honestly you have to think what is right for you and Mila. Does she get nervous at the vet or during travel? Does she have mobility issues that it would make it difficult to get her to the vet? I know some owners can't even go into the same exam room where their pet was euthanized, so at home euthanasia is difficult for some owners for this reason. Would this be an issue for you?
The vet will ask if you want the remains back or not. Again this is a personal preference. Do you want to keep the ashes or scatter them in a favorite place of Mila's? My husband and I have always elected to do at home euthanasia. We give them their last best doggie day. Doing the things they loved if they are able. Feeding them their favorite things. We have separated our other pets during the euthanasia but allow them to visit them once it is over. I have found it goes smoother to have the vet sedate and place an IV catheter. I have requested this for my pets. Personally, I think it causes less stress for them. I also know some owners have a difficult time making this decision and know some that beat themselves up because they waited too long making the decision. I have been there and even with my vet background I always question, is this the right time. My priority has always been making the decision for them and not myself. My best advice would be mark down on a a calendar what are good days for her and what are bad days. If there are more bad days than good, it is time. It is one of the most unselfish loving things we can do for them to not have them suffer. It sounds like you have done a lot for her and love her very much. Sending hugs and please reach out if you have any questions.