Persephoni has always had the ability to transform into an ordinary bunny rabbit to keep close to Chelsea, but up until now that has been the extent of her “morphing” abilities. Finally the question is answered as to whether or not she can turn into anything else at whim. The Elite Guardians are indeed able to change their appearance to whatever they need for a given situation. This gives them the ability to adapt quickly to keep their child out of danger, all while keeping said child in the dark as to the existence of the Guardians.
In other words, Persephoni could easily disguise herself as someone close to Chelsea in order to directly interact with her, but she is required to stay in-character as long as she is visible. This is why she feels like she can “never truly be close to Chelsea,” as she had mentioned in a previous comic.