Tumtitum, I can understand your concern, but a symptom as vague as 'a lump in her stomach', can be anything from the most trivial to the fatal, with an awful lot of other things in between these two extremes.
As others have said, the only people who can help you are the doctors who are treating her.
I do sympathise with you, I had a similar problem when my father was taken to hospital with extreme back pain on a Friday. Preliminary tests were indeterminate and the MRI scan necessary for a definite diagnosis was closed over the weekend so we had to wait until Monday. The doctors said nothing, but they clearly thought it was probably cancer. When the results came back from the MRI scan, it turned out that he had a rare infection in his back that could be cured with a course of antibiotics - and it was.