If your instructor is willing to work in the evenings, I don't think it should be a problem for you to start right away. I got at least half of my 'pre-license' hours at night. You can definitely flight train past an hour after sunset. You can even solo if your instructor is willing to give you that endorsement. I will say that in all of my years flight instructing I never did give the 'solo night' endorsement. However, you could flight train during the week and solo on the weekends.

I wouldn't sweat the $50/hr one bit if you and she click. The flight instruction costs of learning to fly are not great, and a good instructor is definitely worth the extra money. Plus...how much extra will it be? She'll probably get you through in fewer hours than a time-builder. The cost will probably not end up being all that much more for you.

My advice. Best of luck in your training.