It might be a case of "absence makes the heart grow fonder" in this case - they might have gotten used to seeing each other every day, so he doesn't think that blowing a bubblenest is of any use as he isn't going to get her. Perhaps try putting them in seperate tanks, only letting them see each other for a short period each day.
You can condition them at the same time (ie. feeding high protein live/frozen foods or high quality pellets) as they will need the energy for spawning. They may not eat for quite a few days while they are spawning, plus the male might not eat anything for the few days that he is caring for the eggs/fry. The conditioning (and teasing her with the male) will also help the female get fat and produce more eggs for spawning.
May people then introduce the female into the spawn tank by floating her in a separate jar so the male can see her. I use half a 2L cola bottle with the top cut off and holes poked in it - there is a theory that the male can sense her pheromones (that dreaded word again!) which encourages him to build a bubblenest. Do you have anything for the male to build a bubblenest under? The male that I am attempting to breed now will not build a bubblenest - however he goes nuts and builds massive ones as soon as I put a piece of bubblewrap into the tank.
You will also need something for the female the hide in as spawning can get very brutal and bettas don't always spawn immediately after introduction. You will need to be prepared to see your gorgeous girl get beat up - missing fins and scales are quite normal as the male has to show off his masculinity. Some males can get beat up quite badly too - it's really a case of watching them and only removing the female if it looks like she is seriously going to be killed. You can help by only releasing her when she is showing signs of being ready, eg. vertical barring (the horizontal stripes are stress lines, the vertical lines are "come get me boys!" signs)
How big is the tank that you are planning to spawn them in?