Eh... no. She is a SoulForcer, a rather weak one, but she is a SoulForcer. In the beginning she just wanted "to do something", which basically earned her "house arrest" from her father. As a reaction to that she goes into that "spider house" where she gets infected by some sort experimental thing (?) of the NED company that would turn her into something like the human like monsters in the later Candus City dungeons. At this point she already realized her mistake.
Henryk uses this opportunity to see what happened at one of the NED companies laboratories. They find out that one of their experiments, the thing that absorbs Catherine, has broken free. Henryk then orders the player to destroy the laboratory, probably to hide what they did there. In addition the "antidote" makes Catherine into bait for that thing, that escaped the laboratory. Its actually a parasite that adsorbs humans soul force multiplying it's strength in the process.
She also didn't h´just go "lalala-ing". The whole city was evacuated to Grace City but pursued by the mobs due to Henryk turning Catherine into bait. The reason she was so happy is because she somehow got cured and was happy to finally have a friend.
Basically Henryk sacrificed Catherine for an experiment to get himself a promotion. That all happens after she regrets what she was doing. Her last words are actually "Papa, I am sorry".