Traya does have a fleet, remember the Battle of Telos IV? Nihilus didn't come alone, he had a fleet backing him. Basically Traya has what remains of Darth Revan's fleet, which is substantial enough for her stealthy/hit and run tactics.
And I don't know if your aware, or I've just misintepreted. But may I stress this is the Revan of the Mandalorians Wars - not Darth Revan. So he has no Sith, only Jedi. (which may I add, Traya could convert through use of Malachor and her Sith assassins) Your correct though, Revan does outnumber Traya in terms of forces. But I doubt this would be a straight up battle. Most likely Traya would use his forces against him, corrupting his Revanchists and making them fight against him.
That would be Nihilus' forces, not Traya's. The Kaggath is about Traya's power base, not Nihilus', and he tried to kill Traya. And last I saw, Traya didn't pick up the remnants of the Sith Army after Revan killed Malak. The StarForge was destroyed, much of the fleet was gone, and what was left was hunted down. If you're talking about what had been caught in the Gravity Weapon that ended Malachor V during the Mando Wars, that's not really a fleet. Barely a handful of ships. If any of them still functioned.
Also, even as Jedi Knight Revan, his tactics were superb and he's already mastered everything the Jedi Order could teach, including from Kreia. By this time, Revan had already taken the steps towards the dark side on his own after witnessing a vision of the Cathar's plight when he touched the fallen mandalorian womans mask, which he'd take for himself. That was the moment he called himself Revan. It has also been stated in the lore that during the Mandalorian Wars, Revan had visited Malachor V, Dantooine, Korriban, and other worlds where Star Maps had been found, and where the presence of the Dark Side was felt.
Revan is mentally too strong to be tricked by Traya and converted. The only reason Vitiate was able to do so was because Revan wasn't expecting the attack as the Imperial Guardswoman was supposed to help Malak and himself sneak into the Emperor's champers and assassinate him. Neither Revan nor Malak were aware that the Imperial Guard were all linked in a way to the Emperor and their assassination attempt was known to Vitiate before they even entered the building. Revan expected to catch Vitiate off-guard. Instead he was backstabbed by the ImpGuard and got mind-whammied by Vitiate along with Malak.
However, as we saw, this didn't last long. They didn't become Vitiate's puppets. Instead it, more or less, corrupted the pair and made them Sith Lords and Revan decided to conquer the Republic. And yet, despite falling to the Dark Side, Revan was still a tactical marvel and he did what he could to keep the infrastructure of the Republic intact. Unlike Malak who just scorched everything.
So, either way, I don't see Traya being able to overcome Revan, even while he was still a Jedi. Thousands of Jedi had followed him and joined him in the Mandalorian War. Most of'em only died when he ordered Meetra to use the gravity weapon on Malachor V.