At the moment the risk is having to pay a fine that might be INR 500:
Minor suppressions of information regarding marital status / name of spouse etc. inadvertently.
Assuming she can get away with "inadvertently" †.
Leave this to fester and not only might the fine increase merely through the passage of time but it might switch to a higher basis (currently INR 2,500):
In case applicant does not disclose correct marital status and a case is registered regarding marital dispute
In addition, the consequences may become much more serious. For example, if seeking to join her husband should he obtain work abroad, wherever that may be, passport details that do not a match marriage certificate will certainly complicate any visa/residency application and may even mean a visa or residency is not granted.
The damage has been done and she can expect to pay the price for her stupidity at some point. But the longer she puts off doing so the greater the possible adverse consequences.
† If not (and the chances of getting away with "inadvertently" will probably reduce as time goes on):
whoever contravenes the provisions of the Act by traveling without a
valid passport, knowingly furnishes wrong information or attempts to
alter entries made on the passports or travel documents, fails to
produce his/her passport for inspection, knowing uses a passport or
travel document issued to another person or knowingly allows another
person to use a passport or travel document issued to him shall be
punishable with imprisonment for a term up to 2 years or with fine up
to Rs. 5,000/- or with both
So to get it corrected "own up" and go back to where the passport application was made, as you suggest.