Why is y daughter having pain in tooth with molar band on?

Hi, my 15year daughter has had braces on for one year with 4metal molar bands fitted. She has an adjustment every 6-8weeks since the start of treatment and is now wearing the thicker arch wire, usually any discomfort she feels is only for a few days in some of her teeth or all of them, each time is different. She continues to have regular dental checkups 6 monthly (she had one very recently 4weeks ago everything fine and she's never had cavities) She has had another adjustment, approximately 4/5 weeks ago at which she did not have a new arch wire but was given rubber bands to wear to correct a 2mm overbite, since the last adjustment she has had no discomfort this time even though she has the rubber bands but yeaterday(so 5 weeks since last adjustment) she complained of toothache in lower right molar banded tooth which lasted an hour or so. Is this normal? We are worried as she hasn't had any molar pain previously and never in just one random tooth so long after an adjustment, she is due to go again in about 3 weeks time should we go back sooner? Many thanks,Becky