Integrate separate web app inside wordpress [closed]

Yes, it should be doable. And you should be able to leverage wpdb, with new instance, to connect to the separate database. Have a look at this old question, Using wpdb to connect to a separate database.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)