You can dye only one fashion piece at once, so no, it won't work.
I think she's talking about the option to dye a full set. That option exists when you use the regular one-color dyes or the random dyes.
You can't use the full-set option when using regular dyes. The full-set option is only for random dyes. >.<Would be cool if it could be made to work with the random specifics though.
Yes, you're right, I totally forgot about this option. However I did a quick check and it works in a way that the server is checking if inserted dye is entirely random. It won't let any other dye to be inserted, which is ridiculous and in some way defeats the purpose of these new random dyes. It doesn't seem that I can do anything about it.
I mean, not like they're expensive either way... Just buy a crap ton of them and try to get the same color on every piece of fashion you want.