I thought about this, we know that she carried the book through the portal, so when she went through (despite what we saw in the comic book) she might have had a bag full of stuff, including Equestrian coins. Equestria still uses actual gold for their coinage, so a few coins would have set her up rather well to start with. Even if she didn't do a direct exchange for cash -which would have raised a few legal problems- she could have simply sold them to a jewelry dealer claiming that they were old family heirlooms.
I wonder if she owns the whole building and lives off the rent from the downstairs tenant? Her place seemed to be only the top floor.