The floor can be a real killer in these units. If you plan to leave this unit in one place all winter gather a bunch of straw bales together to build a skirting. Or if bales are too expensive you could simply fill lots of big leaf bags with dried leaves.
If the trailer will be driven around, see if you can obtain some old carpet underlay from someone who installs it. They throw out old stuff all the time. Get enough to do two or three layers over your floor.
One important note for anyone reading this. Using a propane stove as a means of heating a trailer in winter is dangerous and leads to excessive condensation. Don't do it. I'm building a very simple thermal mass storage unit and will show you how to do that.
None of what I will suggest in the other post is pretty but it all works. None of it is expensive or difficult to do. I am so toasty warm in my Van that I often sleep naked. But I know other guys who live in the same situation and show up at Starbucks at 5:30 AM to thaw their frozen bones. It's all about good planning.
Let me know a little bit more about your situation and possibly your daughter's condition. If anything is confidential or possibly embarrassing you can do it as a private message. If you're not shy then we will do it here as it may be instructive to someone else who finds themselves out in the cold this winter. If it's okay with you I'll title the posting as follows-- staying warm while living in a tin can/keeping Kathleen warm this winter

. It could be a very useful project especially for you and your daughter.
One man who works for me occasionally has lived on the streets for many years. He has really good camping equipment and claims to be good to 30 below zero. He may be stretching it a little but the point is you don't need to be cold. Inuit hunters are perfectly comfortable in their temporary igloos which are still built when they travel. It's all about being prepared and knowing what to do.