[MattTuck]

I've used those shrink wrap kits before and never found them to be particularly impressive.

If you think the window is the main culprit for heat loss, I'd go all the way and install some blinds (like from select blinds) and a curtain. We have that set up in our nursery, and it is typically 5-8 degrees warmer at night in there, than at the thermostat in the hall (door is shut, but not latched over night).

If you're not sure about the window, consider checking the insulation above her room. perhaps there are some spots where the insulation is uneven, not installed properly. Most heat escapes by rising.

But, if you have old drafty windows, and the draft is the cause of the heat loss, the shrink wrap kit may be the only thing you can do to stop air flow.