A song that gives Kai strength is The Draw by Bastille. This song helps her to keep moving on in life, and not worry about her troubles. Kai is reassured by the lyrics above because she she knows that in the great unknown there is goodness and happy days.
A recent Reddit thread compiled the perfect list of songs that say, in one way or another, that everything will be OK. This playlist will make you smile and remind you that whatever is going on, it too shall pass.