Hi Aline

As far as I know Mittelbau-Dora was a subcamp of Buchenwald not of Auschwitz. There is a website about Buchenwald and Mittelbau-Dora.
https://www.buchenwald.de/en/69/
https://www.buchenwald.de/en/29/

At the end of the war many prisoners from Auschwitz were sent to other camps like Mauthausen, some with trains, but many on the so-called "death march".

The Arolsen Archives have some records of Mauthausen online, but there is also a website about Mauthausen camp.
https://www.mauthausen-memorial.org/en

The deceased of the Mauthausen Concentration Camp
https://raumdernamen.mauthausen-memorial.org/?L=1

Did you seearch with different spellings of the surname on the Arolsen Archives? Sometimes I found one and the same person with different spellings there.

Regards

Corinne Iten
Switzerland