You have to run into at least four of them on your way to the final boss. You can choose to fight them or just run away and ignore them. Two of them (the skippable ones) are team battles, and the other four are duels, fought with your sub-members (they are removed from the party for the rest of the event).
Don’t feel too bad; X6 and X7 were SUCH bullshit games. I’ve beaten X1-4 (and almost X5, ugh), as well as X8 using X with NO powerups (no special weapons, subtanks, life ups, or armor pieces), and I can barely beat X6 to begin with. It’s too bad X6 and X7 were so awful; by that time, everyone ignored X8, even though it was remarkable. I might even say X8 is the best game in the series.
But during the time I played this on the N64 years back, defeating her was like crazy hard! (Beating Ganondorf in the Legend of Zelda: Ocarina of Time, was easier than her!.. seriously.) The first one wasn’t as bad as the second one though! There was heaps you had to watch out for and the air itself slowly lowered your health (because of poisonous fumes.)