Let's take a look at the valid example you gave as well as the other valid permutations:
Aber sie ist zur Zeit Hausfrau.
Aber Hausfrau ist sie zur Zeit.
Aber Hausfrau ist zur Zeit sie.
Aber zur Zeit ist sie Hausfrau.
These are all valid. The difference is in the emphasis. The item in front of the finite verb gets the most emphasis, it's the topic. The item at the end of the sentence gets the second most emphasis.
The iron rule of building declarative clause in German is the V2 rule. The finite verb comes second. Or, to put it differently.
- In declarative clauses, there is exactly one item in front of the finite verb.
Not one word, but one item. For example the subject, an object, an adverbial, including all the articles, pronoun, counter belonging to it. It may also be a whole clause. But only one.
Your example features an exception though. Aber is a so called 0th item, which does not count. These are mostly interjections and particles.
Now you can tell why
Aber zur Zeit sie ist die Hausfrau.
In case you wonder there are two more permutations which should be valid according to the above rule. But they aren't for complicated reasons.
Aber sie ist Hausfrau zur Zeit. (at least uncommon with an adverbial of time)
Aber zur Zeit ist Hausfrau sie. (uncommon apart from poetry)