We have a bunn grxb coffee maker new. the coffee

Check if sprayhead is in place above brew basket.

Either the coffee grind is too fine, too much coffee or incorrect sprayhead. Count the amount of holes on the sprayhead.

Please call Bunn Customer Service. There is a different sprayhead that can be used to prevent this problem from happening and is free of charge.

Dunkin Donuts is a finer ground coffee and the water comes through so quickly that it isn't absorbed quick enough so you don't get the full flavor and it causes an overflow. If you will call Bunn Customer Service, a new flow restrictor can be sent to you to resolve this problem.

These tanks can't actually be overfilled since all water poured in displaces the exact same amount of water coming out the spout. So, whatever amount of water you pour in, will be the same amount of water that flows to your pot minus the amount absorbed by the coffee grounds and filter.

Your problems sounds like an undersized (Non Bunn) filter, or clogged brew basket. To verify this, try pouring in only half the water for your brew cycle and wait for it to finish dripping, then pour in the rest. If no overflow has occurred, you simply have the wrong type of filter. If overflow begins again, you have a clogged brew basket, since no Bunn can flow too fast for the brew basket to keep up with it.

This is because Bunn filters are manufactured differently than generic store bought paper filters. They will flow faster, brew cleaner and stand up better than normal generic filters.
Remember, Bunn makes their OWN filters for good reason.
They made the first, best paper filters for drip coffee pots, and all others are just generic dioxin gas producing paper.

contact Bunn directly for help.

http://www.bunnomatic.com/retail/service/contact.html

Coffee overflowing onto the counter is a common complaint found in response to many automatic drip coffee makers. The following are potential solutions that can be used to rule out "operator error" vs. a defect or malfunction:

1. Don't overfill the basket with grinds.
2. Ensure you are using the correct grind for an automatic drip coffee maker, neither too fine nor too course. (See instruction manual.)
3. Do not overfill with water. Use the carafe to pour water into the reservoir. This is because a "cup" in coffee terms is defined as 6 oz, not 8 oz.
4. Make sure the filter cone/basket clicks into place and that the carafe is centered and pushed all the way in.
5. Try a permanent filter rather than a paper filter or vice versa.
6. Only use the correct permanent or paper filter (see manual).
7. Make sure that the Pause 'n Serve button isn't sticking. (If it is activated too long the brew will escape over the top of the cone/basket. This may be more apt to happen if the alignment of the carafe and the basket is incorrect.)
8. Clean your machine with vinegar or as instructed by your user manual at least three times per year, more if your water supply is hard. A properly cleaned machine is less likely to suffer a burned out heating element, to take too long to brew, to produce "off" tasting coffee, or to clog and overrun the filter basket as the water runs through the grinds.
9. Ensure that the coffee machine is sitting level on the counter.

Some people also try adding fresh grounds to brewed grounds, resulting in an overflow. A restricter valve can be used, but a better solution is to simply pour in half the water at a time. This is what people who buy non Bunn filters do to stop overfills.

Do you grind your beans at home before brewing or is it ground from the store. If you grind just before brewing check her grind and compare it with yours.
Also check to see if she levels the coffee in the basket. Usually when a pot overflows it is because of the grind or the way the coffee sits in the basket.