Welcome to the Asana Community Forum @Taylor_Williams1 
Do you want to add her to a team in your organization or workspace? Because as far as I know it only works for orgs see here.
Do you know if any restrictions were set up for that team? See Admin Console • Asana Product Guide as that could be a reason maybe.
More info on how to add guests can also be found here: Working with guests in an organization • Asana Product Guide
Now if nothing is restricted and you are in an org try adding her to one task or project first then she should receive an email as well.
If not tell her to go to asana.com and then under login „forgot password“. I had this once as well where somebody did not receive the invite email but once they tried to reset their password (they had not set one yet) they got an email from Asana and were able to login.
If nothing helps best to reach out to Asana Support as they have more tools and insight and will surely be able to assist.
I hope that helps 