You could save the file as a clone with no records. Then you have the whole file intact minus any data.
If you can follow Ricks advice, life is much, much simpler.
But if you just want to import a portion of their data model into your existing solution, using FileMaker Advanced, you can copy and past tables from one file to another. But you still have to set up the relationships between them manually. Without Advanced, you can limit the found set for the table to just one record, use import records with the New table option specified to import that one record and then you delete that record. Again, this leaves it up to you to then manually set up the needed relationships.
And then you'd have the task of recreating the layouts from the other file. With care, scripts can be imported from one file into another and all the layout objects can be copy/pasted from one file to another, but it's a detail oriented process where you can save or waste a lot of time depending on exactly how and in what order you import scripts and copy/paste layout objects.
Here's a thread on the layout copy/paste process: Importing Layouts
Given all those complications, you might choose to get that clone and then set up any needed scripts and external data source references to link that file and it's layouts, tables, scripts, etc into your existing system without pulling those objects into your current file.
Rick and Phil--thank you for your quick responses! I will request that my colleague makes a clone of her file and move on to the second solution if that doesn't work for some reason.