My Dog Ate Some Multi-grain Cheerios With Banana And Milk And Now Has Had Diarrhea For Days. I Tried Giving Her Some White Rice From The Chinese Food I Ordered Last Night And I Think That Made It Worse...what Should I Do?

If she is not acting as if she is in pain or really ill, just has the "trots", then just starve her for one day, allowing only water to drink.  This gives the gut a chance to rest and settle down.  The next day give a boiled egg (that you have shelled for her).  The next day she will be mighty hungry and you can go back to her normal food, but give it in small amounts over the course of the day.  After that she should be OK.
If pain or illness is suspected then you ought to see a vet.