Sorry to break it to you, but the Holy Office warned Catholics about these prayers in 1954. When I first heard about them, I did some digging, as I normally do on every visionary I find out about. Here's what it said.
ACTA APOSTOLICAE SEDIS
SUPREMA SACRA CONGREGATIO S. OFFICII
MONITUM
In aliquibus locis divulgatum est opusculum quoddam, cui titulus "SECRETUM FELICITATIS - Quindecim orationes a Domino S. Birgittae in ecclesia S. Pauli, Romae, revelatae", Niceae ad Varum (et alibi), variis linguis editum.
cuм vero in eodem libello asseratur S. Birgittae quasdam promissiones a Deo fuisse factas, de quarum origine supernaturali nullo modo constat, caveant Ordinarii locorum ne licentiam concedant edendi vel denuo impremendi opuscula vel scripta quae praedictas promissiones continent.
Datum Romae, ex Aedibus S. Officii, die 28 Ianuarii 1954.
Marius Crovini, Supremae S. Congr. S. Officii Notarius
Acts of the Holy See
Congregation of the Holy Office
Warning
In some places, a certain little work has been disseminated called the "Secret of Happiness: 15 Prayers Revealed by the Lord to St. Bridget in the Church of St. Paul at Rome", published at Nice and various other places in several languages.
Since it is asserted in this pamphlet that God made to St. Bridget certain promises, whose supernatural origin in no way stands up, let local ordinaries take care not to grant permission for publishing or reprinting pamphlets or other writings which contain these aforementioned promises.
Given at Rome, from the offices of the Holy Office, 28 , January 1954
Marius Crovini, Notary of the Supreme Holy, Congregation of the Holy Office