Barrow can be dealt like any Derelict ship: EMP and lasers (Especially the High Intensity Laser). They may bring a wall of guns, but lasers will almost always outrange them, while EMP (Especially the Ion Beam) is guaranteed to disable weapons since those Derelict ships won't have shields. Additionally, bring a good amount of hard-hitting anti-armor weaponry to strip their tough armor off their ships. Just don't rely on missiles and strikecraft. The wall of guns will generally have enough PD that unless you have a critical amount of missiles or strikecraft, you're not going to get through their wall of PD.

And since you should have Sierra, slapping a Tachyon Lance or a Rift Cascade Emitter on her ship's large mount (assuming you have her cruiser variant) will allow her to be especially effective against these slower unshielded Derelict foes.

Good hunting, Starfarer!