I think it's going to be trial and error. A lot will depend on how carb sensitive Jane is. An 8 - 10% might be OK or you may need to go to MC. If she grazes, it might make sense on the days when she's not bouncing, to give a little less of the MC and as the day progresses, give her LC as the insulin will be wearing off. You may want to look into getting a timed feeder so you can have some control over the carb content of what Jane has access to throughout the cycle if you're not home.
Since Jane has GI issues, if you don't want to use the FF, you could try your own "recipe" with respect to how much Karo to mix in (e.g., 1/2 teaspoon may be HC, 1/4 teaspoon may be MC).