I love using 4A+B when my opponent's back is against the wall cuz it will put me at neutral frames and many people don't realize that. Follow it up with 6KBK and it'll frame trap in many cases. Keep in mind that CH 6KBK can RO. iWR B+K is also a great move, just know that Pyrrha can stab punish it on block.
As for post-GI, Ivy has many great options. The best way to land CS is to buffer the directions BEFORE you GI, and then push B+G after using GI. Here are my go-to options
-iFC 1(B)B, 6B8. The hold scales more but is much more likely to launch. For example, characters like Cervy will not launch from FC 1B at ANY distances, unless he is literally over top of you like when he grabs.
-2B+K, 8A+B because it can RO forward.
-44B+K for the re-GI punish, because the damage is insane and it leads to great wall combos.