A gift related to her new line of work is a nice idea. That would show how much you love and care for her. It would portray your thoughtfulness and good feeling towards her success in life and make for an excellent promotion gift for wife.
You can start by giving her a new wardrobe which is suitable for her latest position. Different types of professional apparels are available in stores and you can gift her something which will prepare her to start her latest venture in the professional front. Silk knitted shirts, sleek skirts, trousers, etc are commendable choice in apparels suited for work.
Otherwise you can present her with accessories which are motivational in nature. An inspiring message namesake or a name bar which has her latest designation inscribed in it can be given to her. The trick is to give something which will make her feel happy. So that she can be sure her husband is quite proud of her and admires her for her achievements in life. It will certainly build the mutual respect between the partners and also enhances their love for each other.
You can also present your wife with things like an engraved business card holder, gravity pen stand, plaques, desk clock, etc which would be useful for her. Something that she can use which will make it convenient for her at work would be a prudent promotion gift for her.
A congratulatory gift basket is a nice promotion gift for wife. You can buy a gift basket and fill it exquisite wines or jewelry or anything that you think that she would like. Just the thought of receiving a gift from her husband will emit a sense of contentment and appreciation from her. So be a little resourceful and try to give her something which can put her in an even more exultant state, even more than the news of her promotion.