Garment Printing - Technical Steps from Screen to Product

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Hello all, I hope this is the right forum, I know there are printing companies on here so fingers crossed. I'll keep the question brief.

If my graphics designer wife wants to send her designs to be printed on clothing, what are the questions to ask the printing company, and the steps to take on her side of things, so that what comes back from the printer has colours that closely match what she created on screen in the first place?

She works in Adobe Illustrator, and I am well aware we are entering a world of RGB to CMYK conversions, colour profiles, spot colours, pantone colours, screen calibration and heaven knows what else.

Thanks :-)