If she likes it, that means it's nice for her, so objectively it's nice.
I am 21 and would not wear it because I think it does look frumpy and I personally care about not looking frumpy Also when I've tried la Redoute in the past the fit wasn't very 'young' IFYSWIM so didn't end up wearing stuff from there. If she just vaguely likes certain features then she could find those in more trendy versions, if that's important to her. Woolen parka-style coats for example.
My rule of thumb is, the more simple the better. Especially with coats which you only have one or two of (usually, at 17) and which need to complement different style skirts, trousers, shoes etc.
I second Zara, my coat this year is from there and I love it. Think they've really got it right with 'outerwear' this year. God I can't wait for the sales!