You have to adjust the Rect of the text element so that it can show the additional text.
Example:Infragistics.Win.EmbeddableUIElementBase embeddableElement = appointmentElement.GetDescendant( typeof(Infragistics.Win.EmbeddableUIElementBase) ) as Infragistics.Win.EmbeddableUIElementBase;
embeddableElement.Rect = appointmentElement.RectInsideBorders;
you would need to do this for appointments also. It just depends what the original text was - if the original text Length is greater than the new text then you need not worry about it, but if it is not then you will need to increase the RECT of the textUIElement.