Its a tough one, and although honesty is always the best policy there is a danger that she may decide to shoot the messenger.

If it was me... then I'd get into the habit of always having some mints around and offering them to people when they come to talk to me. In order to avoid embarrassment to you and your boss, offer them to other people as well (sometimes) but always offer them to your boss.... and she'll probably pick up on the hint.

Some advices from MayoClinic on bad breath:
http://www.mayoclinic.com/health/bad-breath/DS00025/DSECTION=lifestyle-and-home-remedies
1. Brush teeth after eat
2. Floss at least once a day
3. Brush your tongue
4. Clean your dentures well
5. Drink plenty of water
6. Use a fairly new toothbrush
7. Schedule regular dental checkups
8. Chew fresh parsley or suck on a sugarless mint

You can help on items #5, 7, 8, for examples:
offer her (and others) drinks during discussion; inform her (and others) deadline of company free dental services; offer her (and others) sugarless mint.

Maybe not. I mean she is your boss and it may hurt her feelings also. You should give her a box of mint and tell her that it is your favorite and that you bought an extra box for her as well. This way you don't offend her.

Here is some info:

Banishing Bad Breath: Which Breath Mints Really Work

They used real consumer testing and measurements with a Halimeter®, an instrument that measures the amount of odor-causing sulfur compounds in our breath (the underlying cause of halitosis or "bad breath").

Here are the winners:

Starbucks After Coffee Mints came out on top, because it was best at reducing coffee-breath and provided testers with long-lasting freshness. The Halimeter® readings showed that Starbucks After Coffee Mints reduced the most odor-causing compounds in their breath. A 5-ounce tin costs $1.95. Available at Starbucks stores only.

Listerine PocketPaks Oral Care Strips were best at fighting off garlic-breath and ranked second overall. 16 strips, $1.49.

Certs Powerful Mints rounded out the top three, coming in second in garlic-fighting capability. 50 mints, $1.49.

There were also a couple of category winners.

Best to cover up garlic breath: Listerine Pocket Paks

Best to cover up coffee breath: Starbucks After Coffee Mints

Best-tasting mint: Wrigley's Eclipse Flash Strips, 24 strips, $1.49.

Best for odor coverup: Altoids, 1.76 ounces, $1.79.

Testers also found that sugary breath mints tended to create more bacteria in the mouth.

When looking for a breath freshener, look for sugar-free products that contain xylitol, zinc gluconate or copper gluconate, or triacetin and avoid those that contain sugar, maltodextrin, or lecithins, the testers suggested. Of the products tested, Starbucks After Coffee Mints, which contain xylitol, helped keep "bad breath" at bay for a longer period of time.

I would have candy in a candy jar and offer her some. When I was an office manger long ago I always had a candy dish filled and it was free for the taking. offer varieties in the jar and you will not go wrong. You will really score brownie points and get your message across unnoticed if you make sure the boss's candy is included often.

Well, you probably have your boss' email address, and there is a way you can anonymously tell someone that they have bad breath online!

Just go here:

http://www.therabreath.com/tellafriend.asp

Hope this helps and good luck.

Check out http://www.smellyfriend.com/ they will tell your friend for you

Just give her a piece of gun or something :) The sources i have had good success with this website. http://ebestwaytowhitenteeth.com