I think the issue should not be whether or not homeopathic supplements work; it should be that dispensing guidance or advice about their use is presumably not the LW's colleague's job.

If one of the people she provided advice to became sick, or just became annoyed at the money spent/wasted if something didn't work, the company would probably be liable; at the least the LW's colleague could be fired and she should understand that. If she's really that into homeopathy maybe that's the field she should be in.

there may also come the day when someone says "actually it's none of your business what pills I pop" if it's happening on a regular basis!