I think I'm with Kase on this one, maybe for the first time in the sequel series, lol.
Yamada may not have quite hit her breaking point yet, but she was heading there in a hurry. I can't really fault Kase for being a bit short with Yamada, between getting stood up and realizing that her rushing to make the competition would just be furthering her exhaustion. Sometimes a bit of tough love is what it takes to get through to someone you care about.
The mint dying is probably the biggest indicator of how dire things are. Those suckers are hardy. XD