What problems can my sister expect after her colon resection?

Hopefully, none. : The colon's primary function is to absorb water. Therefore, depending on what part of the colon is removed (and how much), one typically moves their bowels more frequently than before surgery; this often improves w/in 6 months. Early on, the main issues will be pain management & getting her diet back to normal. Thankfully, there are very few, if any, long-term consequences.