If you are giving her the medication by a syringe it easy. Hold your snake's body with your forearm or have someone hold the body for you. Gently hold her by the back of her head. She will not like it at all and will fight. You will have to push the syringe through her mouth and she will open it for you.

As for the weird behavior, when things change they tend to become active. She will be her usual self in no time.