Recurring Oral Ulcers: Could It Be Hand, Foot, and Mouth Disease?

My daughter has been suffering from recurrent oral ulcers, accompanied by coughing, with a small blister on her right thumb that is not red or swollen. A week ago, a throat swab test showed no infection of Hand, Foot, and Mouth Disease. However, she has been taking antiviral medication as prescribed by the doctor. With her current symptoms, how could she have contracted Hand, Foot, and Mouth Disease?
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