An interesting look into a less than positive event in their relationship. Good stuff. I'll bet they talked it out more when Kon-san was a little less tired and irritable.
Irritable though she may have been she did have a point, but Ayu-san had a point too that I think I agree with a little more. It's not necessarily about responding to the message but just having received the message and knowing what was going on would probably have been good. Especially with regards to a change of plans on a holiday.