When Ahsoka first appeared, she consistently used one lightsaber in a reverse grip, occasionally switching to a normal/frontward grip when the situation required (It's hard to see, but she is using a backwards grip here. I couldn't find a better picture)
Later, when she had her white lighsabers, she used her previous style of mostly using a reverse grip and occasionally switching to a front grip on one or both lightsabers when the situation required it. She does seem to favor a front grip a little bit more during this period, which makes sense since, as far as I can tell, a front grip is superior in lightsaber v. lightsaber combat since it allows more powerful strokes, but a reverse grip can be more effective for blaster bolt deflection because it favors more movement (speculation), and she would mostly be avoiding using her lightsabers to stay hidden and only using them to fight other lightsaber users until she becomes an open rebel.
During the Siege of Mandalore, once she got her lightsabers back (but blue, for some reason), she began mainly using a forwards grip on her main lightsaber and a backwards grip on her shoto. This change doesn't really make sense, because she wouldn't have had a chance to practice with her lightsabers since leaving the Jedi order, and she is planning to fight someone very dangerous, which is not the time you would want to be experimenting with a new technique. She even does this when being shot at by a large group, when her previous style of two reverse grip lightsabers would seem to be superior. Why did she do this, or is it just my perception that she normally used reverse grips?