The way her employers are deducting tax is the way HMRC do it for me, with more than one source of income. My main job has the tax allowance set against it, and all the others are BR - then it's adjusted at the end of the tax year. If the apprenticeship is the main source of income, then she needs to contact the tax office and explain the position, IMO.
Different people do pay different levels of tax, the colleague's coding might be different due to personal circumstances we wouldn't know about.