We got them some gel stuff which they said has been working.

I'd put your money to work once you understand what you are doing, find some partners that you gel with and complement you and  get in the game.  

But if you have existing granite or plan on putting in granite vs quartz you may want to use general finishes gel stain in the approximate original cabinet wood color.

Purchase price: $127,500 Cash invested: $85,000 Sale price: $257,611 Residential SFH flip, extensive exterior wood rot, original 1950's wiring, nicotine stains from long term indoor smoking.

@Martin Neal I use gel stain on many of my rentals and turn them espresso color.

or would painting over the nicotine without cleaning it seal it in and create more work in the future when she moves out and i repaint again?

Let's go with @scott moron gel football analogy. 

In addition,  gel baits and bait stations should be used. 

The closets will be full of nicotine-infused clothes, and the rooms will be full of nicotine-infused people. 

@Michael Watts I used and thereare posts on the internet regarding General Finishes Java gel stain.