It is not your responsibility to figure out which attorney will appear at the hearing. Whichever one appears or does not appear is the debtor's problem, not yours. If you have a written communication to make, send it to A and B.
The response given is not intended to create, nor does it create an ongoing duty to respond to questions. The response does not form an attorney-client relationship, nor is it intended to be anything other than the educated opinion of the author. It should not be relied upon as legal advice. The response given is based upon the limited facts provided by the person asking the question. To the extent additional or different facts exist, the response might possibly change. Attorney is licensed to practice law only in the State of California. Responses are based solely on California law unless stated otherwise.
The debtor may have more than one law firm representing her. You can check the status of the debtor's lawyers on PACER, https://pacer.login.uscourts.gov/cgi-bin/login.pl?court_id=00idx. but it will up to the judge to make sure these lawyers file the proper substitutions or associations of counsel.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
Attorney A's job was completed at discharge and closure. If the debtor hired a new attorney to reopen, that attorney is now the one to contact. As long as one of them will talk to you, there is nothing to worry about. I have been in this situation before as Attorney A. Attorney B is now responsible.
[This communication is intended as general information and not specific legal advice, and this communication does not create an attorney-client relationship.]