OK, I think there are two different ways. If she already has your name in her "My Family and Friends" list, there is a statement by your name that says "Connect through a Disney account," If she clicks on that it will ask for your e-mail to send you and invite. She should put in the e-mail that you used to set up your
MDE account. You will then get an invite to link/share plans with her. You will find this invite in your MDE account not in your regular e-mail. Once you click accept you will be linked and can share FP+ plans, photo pass etc. The other way is to click on "add a guest" with the little plus sign at the top of your My Family and Friends" list. It will then ask which of three ways you want to add. You can click "By resort reservation number", put in the number and link that way. You will have to get the resort reservation number from your friend. I had to call the Disney MDE phone number to figure this stuff out last week. Good luck!