My mum she is ill what is the Du'aa for her since she leaves in Africa and I leave in Europe.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

Supplicating for one's parents is one of the greatest acts by which one gets closer to Allaah especially if one or both of them are in need for such a supplication, like being sick or the like. However, we do not know a special supplication for one's parents who are far away from their son/daughter. But you can supplicate to Allaah to cure her as soon as possible. It is desirable to supplicate with what is mentioned in the narration of the Prophet . He heard a man supplicating: "O Allaah I ask You, that I bear witness that You are Allaah, none has the right to be worshipped except You, The One, As-Samad (the One Who is free from all needs and all others need Him), Who begets not nor was He begotten and there is none like unto Him". So the Prophet said: "I swear by Allaah in whose hands my soul is, he has supplicated Allaah with His Great Name, if one invokes Him by this name He responds to him, and grants him his request." [Ahmad and others] So it is desirable to supplicate for your mother, but at the beginning of your supplication you can mention the above supplication. You can seek the best time to do that when the supplication is most likely to be answered, which is before the time of Fajr, between the call to the prayer and the call to start of the prayer, etc… Finally, we ask Allaah the All-Mighty, the Lord of the Mighty Throne to cure your mother as soon as possible.

For more benefit you can refer to Fatwa: 88296.

Allaah knows best.