My sister bought a restaurant. She made a contract with the seller. she has been making the payments on time, but she was detained.

The answer is written in the terms of the Agreement.  If your sister's detention or negative publicity surrounding your sister constitutes a breach of the Agreement, then it is theoretically possible that such actions and events would constitute a breach.  However it would be highly unusual for a sales contract to contain behavioral clauses or for any term of the agreement (other than the financial component) to be deemed a material breach.  You should have the agreement reviewed by an attorney and, in the interim, maintain the financial performance under the Agreement.