eyeliner, eye liner

Hi Everyone,

I'm editing a cosmetics manual. "Eyeliner" is spelled with a space in the product name, e.g., GlimmerGlamour Eye Liner. In the body copy, sometimes it's "eyeliner" and sometimes "eye liner". My options are to use "eye liner" all throughout or to use "eyeliner" for the body copy and of course to retain the client's spelling of their product name. I prefer the latter, since product names are the prerogative of the company but "eyeliner" is usually considered closed up (in dictionaries and most writeups, though several cosmetics brands use the open form). What do you think? Thanks!