What Does Recurring Swollen Glands In Neck Of A Child Suggest?

My 11 year old daughter has developed a swollen glad in the left upper part of her neck three times since July. It is quite promounced and accompanied by no other symptoms. She reports that it is sore to swllow when it is most swollen. the symptom seems to go away on it s own only to return a month or two later. My daughter has a history of having ITP at age 20 months old, it was an atypical presentation that resolved before she turned 5 y.o. Her lowest platelet count was 15,000 and that condition persisted for 6 months. I am wondering if this could be a sign of a possible immune sysytem issue.