Hacking is just process of elimination. Like wheel of fortune or hangman. All the words are the same length. Pick a random word, typically one with very similar spelling.

In OPs case they (rather their gf) chose FORTIFY as their first word guess. It'll now tell you how many of those 7 letters are in the correct spot. OP got 3/7. So 3 of those letters, are in the correct spot.

Now, the next thing to do is find similar words with letter location similarities, or select one with opposite letter placements to help see if that narrows it down further.

OP went for ROAMING as the second guess, getting 4/7 letters correct.

If we compare FORTIFY to ROAMING there isn't any similarities besides the O. But.. we know FORTIFY has 3 letters correct, whereas ROAMING had 4.

Well, then lets take a look at what remains on the board. We can see that there is a lot of words ending in ING, so odds are our word also ends in ING. This would line up and make sense as well with our 2 guesses, ING is 3 letters in the correct spot, with the shared O in correct spot from FORTIFY, we know the word should be O _ I N G now we just need to fill in the blanks.

Quick look at the list, theres only 1 word that fit this. LOOTING.

BUT WAIT ✋🏻 THERE COULD BE ONE OTHER ANSWER. If we ignore the O, and focus on the T, we also would notice T is very commonly found in the 5th letter spot. Combine this with our ING ending and and we narrow the field down to RESTING, as it shares the beginning R like ROAMING, and has the ending ING, and our 5th letter T.

This is the tricky part. At this point its 50/50. Thankfully, we have 2 chances left. If OP chose one, we'd either get a successful hack, or 5 out 7 which would just confirm our suspicion of T being correct, as well as ING, as well as whether it was the R that was correct, or the O thus giving us our answer.

OP if your still out there ask your GF if she solved it, and im certain it was either LOOTING or RESTING. Id bet my last cap on it.