is it her first set of extensions. (im not qualified but have read up quiet a lot about this as its something id like to become qualified in) someone with more experience may be able to offer better advice.
a number of things could cause discomfort, allergic reaction to a product used (ie the bonds, or silicon in the micro ring) , the weight of the extensions, tight fitting or not fitted correctly, tension in the extensions fitting. or just the general settling period after having them fitted (a shock to the head/scalp and needs time to adjust)
its normal when extensions are first fitted for them to be quiet close to the scalp as they last on average 3ish months and in this time work down as the hair grows. but the extension should be movable in every direction (up , down , left , right) without restriction or tension and should lie flat against the head (not stick out). slight discomfort (from research) is normal this is normally where your hair/scalp is adjusting to the newly fitted extensions and should settle after a few days.
if the pain is more than slight discomfort or continues for a week or more i would defiantly contact the person who fitted them for further advice.
i hope this helps and hope the pain eases soon