I think the jury is out as a preventative but it is probably helpful once infection starts. Below is a (long) link to a paper about it. It also seems to depend what part of the plant is used in the preparation and so on.
If your friend is taking it all the time I suppose it does mean that she will take it when infected. 🤷♂️
I think using echinacea should really be a short term thing. It's counter-indicated I believe if your immune system isn't great and it can damage your liver.
I have an autoimmune condition and was advised against it.
It absolutely works for me, I take it when I feel the start of a cold coming on. I still might get it but very mildly and only one or 2 days instead of it dragging on.. Being Dutch I was brought up with the stuff and wouldn't be without it. Much better than taking paracetamol etc
I’ve no idea and as I take prescribed medication I do take supplements as they are contraindicated so I really cannot comment on the effects of echinacea. Perhaps Google it??
I have a friend who takes an echinacea tablet each morning from October to March. Is there any research showing whether this really works? I must say she seldom catches a cold.