Definitely talk to her teacher, and the sooner, the better. Other children, or one individual child, might be picking on her or frightening her. The work may be a bit over her head, and “being sick” represents an attempt to avoid admitting that she is having trouble. Also, when you talk to her teacher, you will be able to get a better idea of whether she is pushing your daughter too much, ignoring her or in some other way making school an unpleasant experience for her.
You don’t mention how long it has been since her pediatrician has been seen her, but a current checkup would seem to be in order. After you have done this, unless you find out that there is some physical reason why she claims to be sick, I would get her to school regardless. Say something like, “There are times when we all have to do things even if we don’t feel 100 percent. Sometimes I have to get dinner ready when I would rather go to bed. But unless I’m really sick, I go ahead and cook anyway.”
Whatever you do, don’t let her stay home unless you have convincing evidence that she is really sick. If she does stay home, don’t fill the day with special privileges. Also, without appearing to pry, ask her casually (maybe at bedtime), “Did anything interesting happen at school today?” Perhaps follow up with, “Whom did you eat lunch with?” You may get an outpouring report that no one wants to sit by her at lunch or play with her at recess. If so, you then have something to go on as you pursue it further.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.