Underscores in File names

I'm looking for some documentation to support my position in a "difference of opinion" between me and an editor at my office. She claims that using underscores in file names is not allowed when editing on Avid. I don't know the specific machine/Avid platform she is using but I was contending that underscores are about as basic of a naming convention as possible and should work no matter the platform.

We use PCs and Macs here so I have been developing a naming convention for GFX files that need to go to both avid and PC. Underscores have ALWAYS worked in the past - but they never do when she takes the files. She claims that when she changes the name to remove the underscore - it suddenly works.

Anyone know of documentation I could turn to so I can tell her that there is nothing wrong with using the underscore? Right now she has me creating alternate filenames for her edits and I don't have time to deal with it!

Appreciate any help that someone could offer!