I am so sorry to hear about your Westie's condition.
My name isXXXXX am a veterinarian, and will do my best to help.
There is no pill, at all, for euthanasia.
I get this question often, and it would be so kind to administer a pill at home for a painless, peaceful death.
Unfortunately if there were such a pill, the potential for abuse ( suicide, murder) would be enormous, so no drug company can get a license to make such a drug.
The only safe, humane, peaceful euthanasia is by intravenous injection, using the drug that is licensed for that purpose by a licensed veterinarian. Can you find a house call veterinarian in your area so you don't have to take her to a clinic.
We often go to people's houses for this.
As soon as I get there, I administer a sedative so the dog is not nervous about my being there. Once that injection brings about sedation, I give the IV.
For really nervous animals, I have the dog owner give a pill at home to help with the sedation.
I am not seeing responses from you; I hope you still see what I am writing.
Can you ask your vet to come to the house?
You are not selfish, and not alone. Many people do not want to bring their beloved pets to us for the final visit; too painful, too sad.
Probably half the dogs I put to sleep, are at home.
You are welcome.
Best of luck; I hope you find some one who can help.
My sincere condolences to you.