What Other Measures Apart From Lying Flat Are Advisable For A Patient Having Severe Swelling Due To Cancer ?

My sister-in-law was initially diagnosed with breast cancer about 9 years ago. In the past couple years, it has spread to her pelvic, upper gums , spine and bones but so far no major organs. She has been on major pain pills and intravenious chemo but now is on the pill form of chemo every other week (along with the pain pills). Within the past few months, her legs and mid section have severely swollen with fluid to the point where they look as though they are going to explode. Her doctor ran tests to make sure no vital organs were effected and those tests were negative. The doctor is not sure but believes it may be from the radiation and suggested her to lay completely flat, when she s not standing, for a period of 2 weeks to hopefully bring the swelling down. Do you have any other suggestions as to what may be causing this severe swelling or what to do to relieve this discomfort.