I'm definitely concerned about that heat lamp. Chicks need a small area to warm up, and a larger room temperature area to eat and drink. Do you have a larger brooder you're able to put them in, or are you willing to switch to a heat plate? Heat plates are much safer, mimic a mother hen, and use a lot less energy. I start my chicks in a plastic tote as well and would not feel comfortable with a heat lamp due to how much warmth it puts out. It's very difficult to control in such a small space.
Does every dropping look like that? I see a lot of moisture in it. That could imply the chicks could be overheating and drinking more water than usual. The color itself is not concerning.
If she stops screaming when you hold her, it's possible she's imprinted on you. A few of mine will scream if I'm not in the room.
I will tag a couple of more knowledgeable people to try and help you with her unsteadiness. 
@Wyorp Rock @Eggcessive