My kitten was injured and is pooping blood. No ER vet, what do I do?

Oh no. Poor kitty. : ( There isn't much you can do if there is internal bleeding and a serious musculoskeletal injury here. You just have to keep Tifa in a quiet isolated room and try not to stimulate her much. Bring her small amounts of water via a syringe of small turkey baster and some soft canned food. Getting her seen in the morning is all you can do besides this. I would not recommend giving her any over the counter human pain meds as these are very toxic to cats and can cause acute liver and/or kidney failure.
Best case scenario is that she just has a bad muscle sprain and inflammation of her intestines due to the stress. However, an abdominal radiograph and bloodwork testing needs to be done to determine what internal injuries she has first, so that we know how best to help her condition. I really hope that she will be ok through the night. Lay her in a soft bedding (a couple of old t-shirts and a bath towel can do) for tonight to make her as comfortable as possible. Best wishes at the vet in the morning. Take care.