I bought this miniature rose plant during Mother's day to give to my grandmother and we transplanted it into a plastic pot. Over the summer, the plant flowered beautifully outside in the pot but now that it's fall and getting cold I moved the plant indoors.

The plant had gone through a aphid infestation back in September and last week I suddenly noticed that a bunch of leaves just fell off. I just noticed right now that there is some powdery mildew on the leaves. I sprayed some insecticidal soap on the plant a few minutes ago but is there anything else I can do to make it survive indoors over the winter? I'm pretty sure my grandma isn't overwatering because the soil on top is pretty dry and it's kind of somewhat moist when I stick my finger in the soil. The plant is right beside a south facing window, however the houses behind ours block out a lot of the sunlight when the sun begins to set.