We provide the English and Sanskrit text of Durga Gayatri mantra with swara marks in English provided for easy pronunciation and chanting.
In this mantra, three names of goddess are propitiated, namely, Katyayani, Kanyakumari and Durga.
Below is the English translation of this mantra with swara marks.

Can this mantra include om at the beginning?
I am not an authority on mantras, but usually they are chanted like this only…it sounds, there is no harm in adding Om in the beginning, but personally I will stick with whatever is there till I get some logical explanation about why or why not. Thanks!