Bismillahir rahman nir raheem
Assalamualaikum wa rahmatullahi wa barakatuhu
Yes you can pray for him/her to be guided to Islam, then if he/she become Muslim, you can pray for him/her to be healed. But if he/shepersists in his kufr, he does not deserve to have du’aa’ made for him/her to get better. At the same time, you should still treat him /her kindly by doing other good things for him/her, because Allaah says (interpretation of the meaning):
“… but behave with them in the world kindly…”
“And when the punishment fell on them, they said: ‘O Moosa (Moses)! Invoke your Lord for us because of His Promise to you. If you remove the punishment from us, we indeed shall believe in you, and we shall let the Children of Israel go with you.’
But when We removed the punishment from them to a fixed term, which they had to reach, behold! they broke their word!
So We took retribution from them. We drowned them in the sea, because they belied Our Ayaat (proofs, evidences, verses, lessons, signs, revelations, etc.) and were heedless about them”
And if you want to make him/her ask Allah to guide them to Islam and to straight path.
Dear sister/brotherh hope that help
Asalamuilkum wa rahmutullahi wa baraktuhu
Remember me in ur dua