I am not aware of anything that would allow 2 hotdesk users to login to one phone at the same time, if that is what you are asking?
If her reception phone is 6700, you could create an additional single line key on that extension with directory number 6736. So calls to 6700 and 6736 would go through to this extension.
If the calls need to go through to multiple phones, use a multicall key instead of single line.