Hi, My 13 Year Old Daughter Has Chickenpox. She Has

Hi, my 13 year old daughter has chickenpox. She has had a rash for 4 days now and is relatively itchy. However, what I find worrying is that she is complaining about a severe pain in her ribs. She does not appear to be short of breath, but is very lethargic. Should I be worried? Is it best to take her to a doctor?