It says in al-Rawd al-Murbi‘ wa Haashiyatuhu:
“He has the right to stop her hiring herself out” because he will miss out his rights as a result of that, so it is not proper for her to hire herself out except with his permission. But if she hired herself out before marriage, that is valid and binding.
It says in the footnote or commentary:
i.e., her employment is valid and the contract is binding, and the husband does not have the right to annul it, because its benefits were acquired by means of a contract that came before his marriage contract.
End quote from Haashiyat al-Rawd al-Murbi‘ by Ibn Qaasim, 6/444. See also al-Insaaf, 8/267
Shaykh Zakariya al-Ansaari (may Allah have mercy on him) said:
If a free woman hires herself out to do a specific job, as a wet nurse or for any other purpose, without the permission of her husband, that is not permissible, because all her time is devoted to fulfilling his rights… But with his permission it is permissible.
If he married her when she was employed, he does not have the right to stop her from fulfilling the terms of the contract to which she is committed; this is similar to the case if she hired herself out with his permission.
End quote from Asna al-Mataalib, 2/409.
Based on that:
The husband does not have the right to take her away from the country in which his wife is required to stay according to the terms of the contract that he knew about before he married her or for which he gave her permission.
It says in Minah al-Jaleel:
If a woman has committed herself to working as a wet nurse, and her husband wants to take her away from the land where the family of the nursing infant lives, if she hired herself out as a wet nurse with his permission, he does not have the right to do that. But if it was without his permission, then he does have the right to do that and the contract of employment is annulled.
End quote from Minah al-Jaleel, 7/471
Based on the above:
The matter is between the husband and his wife. If she agrees to give up her job in order to travel with him, then she has done well. But if she does not accept that, then he can look for a suitable job in the place where his wife lives and works.
If he does not agree to that and he wants to divorce her, he does not have the right to withhold the mahr that he agreed to give her and she is not being wilfully defiant (naashiz) by refusing to give up her job. Rather he may either keep her or divorce her and give her the right that she has over him, which is half of the mahr stipulated.