Serena was pretty clearly a rather timid person, only gaining the true confidence she needed as she journeyed; in that case, it's not exactly easy to stand up to the mother that loved and raised her, even if her mother's profession wasn't what she wanted. Besides, her mother was pretty headstrong and stubborn, as well, so that probably made things harder.I recall her wanting to reunite with Satoshi as well when she saw him on the news broadcast, so I'd say that he was a major motivating factor in Serena's desire to go on a journey. As for Serena not wanting to follow in her mother's footsteps, I never understood why she didn't simply put her foot down sooner.