I like your poncho/shawl idea ^_^.
I agree with your Mom about trying to re-use the same fabric for the ears and tail, however I'm personally a fan of faux fur for that sort of thing. I'm sure that so long as the colors match closely enough you'll be fine using whatever material you're comfortable working with.
As for the style of the tail, I would think about whether or not I plan on sitting-down at all, look at some tutorials, and make my decision based on personal preference. I was recently turned-on to cosplaytutorial.com, and highly recommend them as a resource for great tuts! Here's a link to their section on tails: http://cosplaytutorial.com/list.php#furtails
They have helpful wig tuts as well: http://cosplaytutorial.com/list.php#wigs
Hope that helps!