Fighters and Ramming ships. And everything else everyone else said too.
Tis very hard to overcome the RT, but if you can find her ship yards or production worlds, go after them with all you have. Force her onto the defensive. Mine the hell out of every WP planet and sector you can. Force her to have to produce other ships.
Additionally, use drones if you can to attack her ships from a sector away or so. Target her worlds and if you have to, lay a trap.
Build a starkiller and cloak it next to a star. When her ships enter that area, even if you have worlds, take them out. (Last ditch effort, but very effective in the end game.
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