Point 1: Why would you be blocking indefinitely? After you block it, you'll be back at neutral. The dive is minus on block, so she can't do anything after it. And you probably should be spacing out your jC better if you are being thrown out of it.
Point 2: You are talking about Tsubaki's cross over shield rush move(236D), right? You can just IB->backdash. Of course, you can always just block it and wait until Tsubaki runs out of charge so she can't do that anymore.