While it is easier to zone Arakune than the rest of the cast, it doesn't work forever. Eventually the Arakune will wise up to the lobelias and be able to summon the curse cloud without getting interrupted. Depending on which cloud is summoned, this situation can be very bad for Rachel, as her movement isn't very... good. In this sense, I agree with Jason D. and say go for offense. (After a bit of zoning to feel him out.) If you run up and fight Arakune without curse, there isn't a heck of a lot he can do outside of trying to anti-air you or use jB. When in close quarters, be sure to stay unpredictable and use 236A at close range to counter his 2C and jump out attempts. Before rushing in, it is a good idea to have a few poles in his vicinity and maybe the pumpkin to back you up. The situation feels pretty in Rachel's control when you're fighting Arakune with no curse meter.
If you happen to get cursed, I find the first thing you should try is to jump the hell off screen. SJ.8D 8D seems to work nicely, then rapid input 236C to stall even longer. (Also, be weary of any bugs that attempt to fly upward at you as you do this.) If you get put in blockstun, its pretty rough, as we all seem to agree on. I like to try and 2C Arakune's overhead/dive attempts to get him off me, then just go into air combo from there and run away again. A general rule is, if you're about to be cursed, conserve as much wind as you can and be prepared to run the fuck away.