FONTS SUBSTITUTING!

Hello!

I am working on a project for a client. It's in InDesign, DPS. She has supplied me with all the fonts. I've installed them and when I design the pages everything looks as it should. When I send her the InDesign files back, the fonts are substituting and she needs to adjust the layouts slightly.

I need to avoid this and find out why it's happening!

Any help is greatly appreciated!

Thanks!
L