Bringing outdoor plants inside can also bring in all those pests that nature controls outside but can quickly get out of control inside -- spider mites, aphids, fungus gnats, etc. If you get the sister plant I would consider never planting it outside this year and just growing it indoors until next spring.

don555 makes a good point on the sister plant by keeping it indoors. What I do in the fall is pull all my over winter plants a day or two before a stretch of very cool nights or just one night in the lower 30's or below. You kind of play it by ear and watch the forecast. Even if you get 75 on Halloween, you might have three nights at 30 degrees a week before that and the plant likely wouldn't make it to Halloween at all. 40 degrees is kind of a line in the sand for me. A night or two slightly below that and I probably won't pull them, but more nights or much lower and I call it a season for the overwinters.
Bruce

thank you for the tips, I'll keep it inside then. Both plants had aphid problems from the soil but haven't seen any in weeks. Should I transfer it to larger pots so it can grow or keep it a managble size till spring?