Hi crystalrose,
It is not uncommon for one alter to be obsessed with sex. It is very possible that she has experienced sexual trauma. That is where they may have "learn" it. They desire and need love and that is the only way they know how to obtain it. However some may confuse lust with love. They will not be shy which is good, however they will get the host committed to some activities that host and other alters do not care for. You must be careful because the alter will try to stay out for longer periods.