I need to physically get my aunt to go to a nursing home, but she is unwilling. Any suggestions?

Is there a possibility that you Mom would agree to move into an Assisted Living facility so she can still "help" with her sister but she will get help as well to do the things she can not do with ease. It also sounds like your Mom could use some help as well.
This might be a Win-Win for both of them and maybe even you, if your Mom is comfortable and gets help herself she may decide to stay which would take a care-giving role from your shoulders.
If that is not necessary your Mom could move out after her sister passes.

Would a little bit of trickery help? If she was told that it was only temporary until your mother can get back on her feet?

My Mother is ill, 87 years old and not capable. I believe we are going in with the caregivers respite then hoping she adjusts and stays to be with her sister.
My thanks for all the suggestions. Hope I can pay it forward.

Based on personal experience, be firm and tell her she has to go and why. If she refuses, try this tactic - it worked when my husband was very ill and refused to go to the doctor in Philadelphia who discovered he had cancer. I told him he could go with me willingly. He refused. So I asked him would he prefer I have two men who I (I pretended about that) hired take him to the doctor. He finally gave in and went with me. You may have to consider getting help in physically getting her to the nursing home. Or an ambulance may be the solution. I don't know anyone who willingly will go to a nursing home because I am sure they realize it is the beginning of the end and a death sentence. It would be that for me,.

You really can't prepare her emotionally, unfortunately. You likely will succeed with using a respite plan then leaving her there by continually telling her that your mom is not well enough to take her back yet but that you are working hard towards that end. They will likely tell you and your mom to stay away for a while, but you do what you feel is right for her. If you think she's better with one of you visiting, ignore the facility and go as often as you see appropriate. Good luck!

Dear Juliet,

I'm so sorry to hear what is happening. What an amazing mother you have to been so loyal and devoted to her sister's care. I know change is hard. I think your 97 year old aunt must be so scared. Are you able to have independent third party talk to her? Maybe a social worker, family therapist, family doctor or counselor could help her with the transition. Hopefully they can allay her fears and help her cope with this change of care.

My Mother feels trapped. She is a cancer survivor in remission. We want my Aunt to have the best care and we can no longer provide it for her in her own home. My Aunt is terrified to leave her house. I am terrified of losing my Mother. The plans are made but you cannot force a person to go unless you have guardianship. I am hoping we get a social worker that takes the time to understand the situation.

Juliet, not to nag you but that is quite a "politician's answer" to the question of what your mother wants :)

If you don't mind humouring me: does your mother agree that your aunt needs to be placed in the Nursing Home? I am getting a vibe that you think she does but... just short of saying so. Especially to your aunt.

Whose house is it, by the way?

My Mother wants her to be with her sister in the nursing home. Everyone but my Aunt agrees she needs to be in a nursing home. Two doctors. Getting hospice to assist.

I really just wanted advice on how to emotionally prepare my Aunt.

Thank you country mouse for your concern.

There's another sister already there?