I'm not sure if El Salvador they handle things similar to the US. In the US if some one has not had any activity in an account for a while or something similar - it goes to the abandoned properties list. The state Treasurer's Office will have a list of "abandoned properties" that you can claim and find by going to the appropriate website.
I know you said that you have had activity on the account, but perhaps if the bank simply made a mistake, they may have classified it that way?
I figured it was unlikely your mom was involved in anything shady - just kind of thought it was funny to find that article. That was what clued me in that it was a national bank as it was described as the largest national bank in El Salvador.