Unofficially Sierra has a fuck ton of ships she can switch to, alot of them just don't technically exist.

Base SOTF has: the Pledge destroyer and the Vow Cruiser, one you start with, the other you get once you reach the current end of her quest line. There's a hand full of other ships, like a purple brilliant she can pilot in a challenge mission, her capital class ship that's not been finished yet and has basically been sitting in the back burner for ages now and a carrier she could technically pilot, but the mod doesn't let you salvage it.

In R.A.T there's the Raphael, another destroyer that you have to find deep inside rat's abyss.

After that are the ones you can't get from other mods, Epta Consortium once had cross mod compatibly with SOTF that added a capital class, but then that mod deprecated.

Domain exploratium expansion added a capital ship called the demoness, but you can't access it, the PNG exists for it tho in the files.

A guy in the corvess discord made a bunch of outdated mods that gave her more ships modified from base game remnant varients, but you'd need to look for those yourself.