All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
In principle, a woman should not travel without a Mahram, because that is forbidden. The Prophet said: “It is not lawful for a woman who believes in Allah and the Last Day to embark on a one day and one-night journey except in the company of a Mahram.” [Al-Bukhari and Muslim]
Based on this, your wife's journey to the land of non-Muslims without a Mahram is forbidden for two reasons:
1) Traveling to the land of non-Muslims.
2) Traveling without a Mahram.
Since necessary medical services are available in your country, there is no need for her to travel to a non-Muslim land without a Mahram.
For more benefit on the prohibition for a woman to travel without a Mahram, please refer to Fataawa 262621, 88562, 193077, 102095, and 85945.
Allah knows best.