Hello @Ken302,
You could try the following
1) when logged in to your account, remove her as a co-host
2) when still logged in to your account add her again as a co-host
3) she will have to reply to the email on her device when logged in to her own Airbnb account.
If that doesn't work you'll have to contact Airbnb support to discuss the issue.
For information on ways to contact them type "contact airbnb" in the "Search the community" box on these forum pages where you posted your question. Scroll down a little in the list of suggestions that appears and click on the "Contact Airbnb: A Community Help Guide[UPDATED]" one. That lists phone numbers and ways to contact them via Twitter or Facebook.
Steve.