Discovered Hard Painful Lump Under Arm Pit. Changed Deodorant. Suggest?
Given her age, the chance that this is a problem related to her breasts is almost zero. Given your description of the location of the lumps, these most likely represent lymph nodes. These could simply be a sign of an infection (some viral infections can do this, such as mononucleosis) or a sign of a blood related disease.
The main argument for having someone see her now is:
1. London certainly has good hospitals and everyone speaks English
2. It would be good to see the lumps while they are present, so that they can be described and documented for future reference
3. They can potentially draw blood and determine whether it is safe to wait until 8/9 when she can see her regular doctor
I sincerely hope that this helps!