I don't know if this has been made somewhere down the line, if so, I'm sorry.
The retainer itself is a great concept, and I like how he/she acts as a bank and market at the same time, but when it comes to assignments it seems like something of an annoyance because I honestly forget that she's there unless I need to sell something.
There have been times where I send her out on a 1h mission, and completely forget about it and don't bother to check her until a day or so later. To the market leech, or the bored random person just standing around a main city that might seem bizarre, but I'm one of those players who are constantly out and about enjoying my time online, getting achievements, running dungeons with friends and such.
So my suggestion is, can we get a small blinking icon that lets us know when she's done doing whatever she was sent out to do, it could be attached to the mini map, it could be its own hud icon that can be moved to wherever. I'd even go as far as to say put an item in the game that lets us summon them wherever we are but doesn't let us access the marketboard, maybe just the ventures and bank, or just the ventures themselves.