Yes, her mood could be in response to her father canceling is time with her. If she is reacting to something that most people would react to, like a disappointment, then most likely she is having a normal reaction to the situation.
If she is saying she feels fearful and there is no direct reason for her to feel this way, then she may either feel sensitive to the situation, or she can be developing fears. If it seems that fear is taking over her life and she is unable to function because of it, that can indicate a more serious problem. But if she just expresses fear in certain situations, she may just feel upset about her situation and that is probably a normal reaction.
Here are the symptoms of childhood Bipolar (since childhood Bipolar symptoms have not been established yet, these are based on the research there has been and adult symptoms of Bipolar) from Psychcentral.com. They may seem similar to normal childhood reactions so you may have to keep an eye on your daughter just to see if the reaction solves itself or may need further evaluation.
Because the current diagnostic manual of mental disorders doesn't recognize childhood bipolar disorder, there is no official symptom criteria. However, researchers have used criteria similar to that of adult bipolar disorder, requiring a child or teen to meet at least four or more of the following:
Keep in mind that many of these behaviors, in and of themselves, are not indicative of a possible disorder and are characteristic of normal childhood development. For instance, separation anxiety, by itself, is a normal fear of being separated from one or both of the parents (for instance, attending the first day of first grade or if the parents want to go out for a night).