No. She has no power in the Inquisition and I believe she dislikes it.
In your Inquisition yes. In my Inquisition, Vivienne is the only one together with Cassandra and Varric that support the Inquisition the most. I've circle mages, templars and most people join the Inquisition as agents because of them. These three are the ones who contributes the most to the Inquisition.
The rest... are like nothing they are actually sticking around to be safe... Ironbull is a bodyguard, that's it...Unless he betray the Chargers that way I'll have the Qunari at my disposal.
Dorian I wonder how the Inquisition will help restore order with just one tevinter mage who is not loved in his homeland, Sera bleh... Blackwall is a thug and a nobody too, Solas nothing,.... just talk and advice.