The official Marvel Tsum Tsum Game site has just announced
that starting tomorrow (so midnight Pacific Time) Spider-Woman, Spider-Gwen, and Silk will be added to the orb box. From Sept 30th until 11:59pm (PT) on October 3rd they will have a higher than normal drop rate from the orb box.
In addition, until the end of October (11:59pm Oct 31st PT) their HP, ATK, and DEF will be boosted by 500!
They also posted preview videos: