My Sister Recently Had Spinal Surgery To Correct Mis-aligned L5/6

My sister recently had spinal surgery to correct mis-aligned L5/6 discs. The pain in her back is now gone but she has had fluid build-up in her thighs and groin area ever since the surgery and muscle spasms in her things and groin that are quite intense whenever they occur. A strong diuretic has not worked. Could you tell us what might be going on? She is in a rehab facility now.