If you're sure it wasn't an original design, you're probably okay, but since you know it was made by a fellow member, why not ask next time just to make sure. A simple PM saying you loved her quilt and would like to make one yourself, would she mind if you used the same colors would probably make her day.
With original designs, copying without permission is not considered flattery at all...it's stealing. Selling or personal use has nothing to do with it.