How can I upgrade a sub-users account?

It is telling her that she as reached the limit of forms she can create.  We are collaborators for same client.  I have very large plan and purchased a smaller plan for her.  She needs to be able to create her own forms and share them with me and I need to create forms and share with her.  

Do we both need the most expensive accounts? Our company has a small budget. 

Add the account as a sub-user:

https://www.jotform.com/help/232-How-to-Share-Forms-with-a-Sub-Account-User

Then  once the account is added, the sub-user can drag their forms into the shared folder to transfer them to your account.  In the My Forms page, just drag the form title into the shared folder and the user will be prompted to confirm transfer of ownership.