First let me say that I hope you, your partner and her mom are holding up okay. Stress related to this illness can be huge, so be sure to take care of yourselves as best as possible, using support groups and talking honestly with one another about your fears, hopes, etc.
Tarceva may be the next option. I have Stage IV LC and was put on Tarceva immediately, no Intravenous chemo. Tarceva was designed as a secondary line of treatment after chemo is no longer working. It is a "maintenance" drug as it does not "cure" your lungs of no cancer, just prevents it from growing and spreading. In some cases, the cells shrink too, which is great, but rarely, do the tumors go away entirely. I have been on Tarceva for a year with great success, and only a few side effects (hair thinning, skin rash/acne for about three months, and sometimes GI complications).
Let me know how things progress for your partner's mom. Keep Smiling and having faith.
ann