As far as we saw in Rebels, she only trained with Kanan. Sabine only found the Dark Saber well after the events at Malachor, which was the last we really saw of Ahsoka in Rebels until the bits in the last few episodes, so didn't train with Ahsoka. I'm a little puzzled by the whole "walking away from you" and "Master" bits in the trailer, since they didn't really have a relationship other than fellow insurgents in Rebels.

Anyway, I would expect Sabine to have lightsaber skills similar to Bo-Katan's, given that Bo-Katan likely trained with it more than Sabine did (though, on the other hand, Sabine had some instruction from an actual Jedi). She has her Mandalorian tricks (like the cable gun, flame thrower, etc.) that should make it a more interesting fight with a Force wielder, but she'd be outmatched.