What is the opinion of Sharia regarding dealing with a relative who has bad conduct and practices sorcery against her relatives who have severed ties with her due to her bad conduct?

You must be deliberate and not accuse your sister of sorcery without conclusive evidence, for the Qur'an and Sunnah forbid suspicion. Approach her and advise her with what pleases Allah, for she may not be guilty. If she does not respond, and you become certain of her practicing sorcery, then beware of her while maintaining kinship ties to the minimum extent, such as phone calls. It is permissible to ostracize her if it will stop her from her disobedience; otherwise, it is not.