Hard to tell. The breasts are generally quite lumpy. Does she check herself regularly for lumps? Is the lump normally there or is it unusual? There are hundreds of questions!
If you are really unsure she can go to the Nurse at her doctors and they will check for her
I thought i had a lump too, but I told my mum and she felt the lump and said it was normal and she had the same in hers, which I felt too, but still check it out but try not to worry.