Can't the baby car seat fit in the trailer? Think how safe she'd be if you could attach it to the trailer (cargo strap?) and put her in the 5 point harness of the car seat.

My baby trailer has a soft bottom (I use it for my dog), and I undid some screws and disconnected the little sling seats so I could put something stiff in the bottom for the dog (used pillows, but I want something else). If your trailer's like that, then the car seat might not work. But if it's a hard bottom trailer, I'll bet you can work something out.

Karen