My Aunt wants to take her dog back that she gifted me. Please help, absolutely devastated?

So my aunt decided she didn’t want her 4 ur old chihuahua anymore cause she wasn’t home enough to take care of her and was going to Europe for a month. I offered to have her and she gave her to me saying it was a PERMANENT thing.

it has now almost been 3 months since we’ve had her, I absolutely adore her so much and love her with all my heart. I just lost my 15 year old dog this February and was devastated so she really helped me heal. She is saying she wants her back and I keep saying no but she is still asking whenever we talk?

am I the ass hole for saying no?

she is registered under my name now she she is my dog.

Updates
+1 y
She did have her for
About 4 years
Updates
+1 y
To clarify:

My aunt is very very wealthy, her and her husband earn over 500k a year, so she can get a new dog without question.

She gave her to me because she said she was never home to look after her, the dog was alone a lot and not getting much attention and because she was going to Europe for a first class holiday she wanted to SELL her dog online But I offered to take her. She agreed this was a PERMANENT thing.
I guess she just misses her. I absolutely love and adore her
My Aunt wants to take her dog back that she gifted me. Please help, absolutely devastated?
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