my friend and i were stopped for weed and i want to take responsibility and get her off the hook

Normally your taking responsibility for contraband will not get the charges dropped for your friend. The definition of possession is to have the ability to exercise control over the substance. If your friend was aware of the "weed" and had control over it, or the ability to exercise control, such as having the ability to hold, touch, smoke, or otherwise have dominion over the weed, then he or she possessed it under the legal definition of possession. That is why both of you were charged.  I had a similar case that went to trial, both people in a car were charged, and at trial, one offered to take responsibility for the pot, and even said that the other was not allowed to touch it.  However due to the location in the car (on the dashboard in plain sight) the passenger was found to be in possession, and had the ability to exercise dominion and control over the contraband. He was found guilty by a jury and got 6 months jail.