Wheras generally in German business communication the Sie is preferred, especially in the so called "creative" businesses such as graphic design, advertising, web-design, web-publishing and programming, and also in the "ecosystem"1 of startup enterprises, using Du is very common now. You even can see it as the standard.
As your friend offers her services as an illustrator, she is pretty much in the center of this "creative" sector of the economy, and thus Du would be very much the expected form of addressing everybody.
I suppose that most people in that business would rather be estranged by being called Sie by peers (i.e. co-workers, colleagues, clients, suppliers). However, things always depend on where one locates oneself. There may be very well-established advertising agencies that insist on calling everybody "Sie" especially when they have very high-level customers such as the large publicly traded companies with their strict hierarchies (and managers that earn millions). People in such organisations tend to prefer the Sie, unless some modernistic company culture is imposed on them to use Du, or their lingua franca is anyway English which makes the topic meaningless.
Consequently: addressing your friend by Du is not blunt, it is just like the counterpart is used to do it, obviously including trying to send a message like "we are a young, cool, uncomplicated company". Your friend may simply answer by Du, too. Answering with Sie would probably make people on the recieving side rise an eyebrow.
1) Calling one's business environment an "ecosystem" has become a hype recently especially with startup people.