Yes you should be aware that your patient has MS. This can affect muscle tone (e.g. spasm) because of pain generated by the ankle. altered sensitivity, reduced propriocepsis. Medication she is taking could also put some obstacles in your way.
Taping or splinting can potentially have a negative effect (increase of sensoric imput in the area of the ankle).
Could try to reduce any spasm by getting limb out of pattern of extension hip and plantarflexion-inversion ankle. the knee and hip may go into flexion though but this is a wild guess. In general chose a tactic which avoids pain.