gotta preface this with a disclaimer: I don't know marisa too well.
Marisa is a bulldog of a character who specializes in attacking the opponents drive gauge, vs Gerr84 starting the round passively was great!
But the strength of Marisa lies in her amazing special moves that need specific answers and awareness to keep in check, like light phalanx or charged gladius that deal insane drive chip on block and force the opponent to make a defence decision: respect the pressure and get burnt out or start parrying to protect their gauge and leave themselves open to throw mixups.
Try loading into games, win or lose, practice landing spaced slightly charged gladiuses. This poke is great because it does its chip damage on block, pushes them closer to the corner on hit and even gives you the option to leave a spacing trap for the opponent to fall into with st.mp afterwards.
You'll probably lose a few rounds before you really start to intuit where the move is best used