On that note of DP > Bufudyne ---
If you don't want to guess when she has 50 meter, just mash Dia on the way down. If all she does is DP, the Dia will hit her. If you're in the corner you can super cancel to Agidyne if it'll kill or you otherwise find it favorable to you.
If she does DP > Bufudyne, Dia will eat it and you can land and do a counterhit punish combo (5B CH 236D ....)
Just be sure to hold Dia down just a smidge, cause if she does D Bufudyne, the delay will hit you unless you hold Dia for a bit. With C you can release Dia as soon as it becomes active, but holding it a little won't affect your ability to punish it anyway.