Please need Advice

My daughter was diagnosed with melanoma in August. 2016.  Her melanoma was just under 1mm and had it completly removed.  She also had the setiinel lymph node removed which came back with micro cluster of cells.  She is being seen at Sloan Kettering in NYC.  At this point she is not in amy treatment, but is due for a brain MRI, pet scan and ultra sound of under her arm where the Sentinal lymph node was removed.  She did have an ultrasound in December of that area and it came back clear.   After the Surgery she had numbness under her arm, which I know is normal.  In any case for the last week and a half she has been periodically feeling aware that something is different in her armpit.  She is not sure if she is just noticing this because the feeling is comng back in her arm or if it is new pain.  She feels a subtle ache in the area in her armpit where the lymph node was removed.  in the last few days she has felt the sensation of it being swollen, though it doesn't visually look swollen and there are no visible lumps.  It is tender to the touch.  She lives near my other daughter who touched the area that she fees is swollen and she did notice that the tender area feels slightly firmer that\ the unaffected side.  We have an appointment scheduled in 3 weeks for all the tests.  Just feeling so so anxious.  Any suggestions, advice…….