The MOST appropriate isometric movement for Juanita to try, given her need for low-impact exercises during recovery, is wall sits.
Wall sits involve holding a seated position against a wall, which engages various muscle groups without the risk of dynamic movements that could exacerbate an injury. The other options, such as sit-ups, walking, and bicep curls, are not isometric exercises or might involve more movement than is advisable during her recovery.