Is my lack of communication with my sister, who married someone I disapprove of and who appointed her maternal uncle (khal) as her guardian, considered a severing of kinship ties, and is her marriage valid?

Marriage is not valid without a guardian (wali), and the brother is a guardian in the absence of the father and grandfather. If the guardian withholds consent for his female ward (adhl), the judge marries her off. As for the girl, she is not permitted to conduct the marriage contract herself or appoint someone to marry her off. If the marriage takes place without a guardian, or authorization from a guardian or a judge, then the marriage is invalid. The brother must maintain ties with his sister, and it is forbidden for him to sever them. Maintaining ties refers to common practice, so if lack of communication is considered abandonment and severance in common practice, then it is forbidden, and he must communicate.