My mom once saw this horror movie when she was young.
It’s about a couple visiting a castle. They are not allowed in one certain room. In that room lies the embalmed body of Anna (or maybe Ana). Anna looks just like the woman from the couple.
Later, the couple goes home again, but the woman from the couple isn’t actually going home: it’s Anna.
“Black Sunday”(1960)?
Barbara Steele plays an evil witch named Asa and her lookalike descendant. Not all the plot points you mention match up, but below is the IMDb page:
https://www.imdb.com/title/
Ok, something went wrong. Here again, maybe, is the IMDb page:
http://www.imdb.com/title/tt0054067/?
Another maybe is Tomb of Ligeia. It is in color though. The ending suggests Ligeia is the one that survives and leaves the castle.
“Crypt of the Vampire” (1964)?
The plot is similar but the woman is named Laura.
https://www.imdb.com/title/tt0057280/?ref_=nv_sr_1
This may not be it, but it sounds like an adaptation of Carmilla.