Please don't worry about your daughter's breast lumps.The changes she is going through are extremely common at 11, because at this age her hormones play a big role during puberty and making breast lumps much more likely. Feeling a lump or lumps in young girls is inevitable and it's part of growing up.Actually,the most widespread type of breast lumps at this young age,are typically connected to normal breast development and growth and certainly not breast cancer.
Advise your daughter to limit chocolates and dark colas as caffeine might increase pain in her breasts .
If these lumps persists or seems to be getting bigger,I would advise you to take her to her pediatrician for evaluation and to check if there are any other signs of puberty or other possible causes for the lumps.
Best wishes to both of you. :)