Depends which dialogue.. she complains more than once. But Catherine is not required to progress currently. This is more a bit of foreshadowing for things to come.
She will be available again after the growth-events have all been handled. Post directly below should give hints on how to complete it. Unless you haven't seen the Yuri-Scene yet. Then you need to buy the potions at Lucias and bring the remaining one to Stella to start the growth events.
