I will qualify my response with a caution that I do not know what the laws in your state are, specifically. Nevertheless, I think your girlfriend has been grossly misinformed on this subject! All too often, CJ majors and Law students have great ideas of what the law is like, and no real practical working knowledge of it!
At least in my state, you are absolutely allowed to defend yourself with a gun if you are attacked with a knife. Justifying the use of deadly physical force is often much tougher for those of us in law enforcement (if only due to the nature of our jobs and interactions with crazy people). All the same, many of our officer-involved shootings have involved suspects armed with knives! I almost had one earlier this week!
In my state you also have a lot more leeway in the use of force within your own home (these are the so-called "castle doctrines" that many states have)
Just for sake of example, here is the exact text of Colorado's two statutes concerning the use of physical and deadly physical force against an assailant:
"18-1-704. Use of physical force in defense of a person.
Statute text
(1) Except as provided in subsections (2) and (3) of this section, a person is justified in using physical force upon another person in order to defend himself or a third person from what he reasonably believes to be the use or imminent use of unlawful physical force by that other person, and he may use a degree of force which he reasonably believes to be necessary for that purpose.
(2) Deadly physical force may be used only if a person reasonably believes a lesser degree of force is inadequate and:
(a) The actor has reasonable ground to believe, and does believe, that he or another person is in imminent danger of being killed or of receiving great bodily injury; or
(b) The other person is using or reasonably appears about to use physical force against an occupant of a dwelling or business establishment while committing or attempting to commit burglary as defined in sections 18-4-202 to 18-4-204; or
(c) The other person is committing or reasonably appears about to commit kidnapping as defined in section 18-3-301 or 18-3-302, robbery as defined in section 18-4-301 or 18-4-302, sexual assault as set forth in section 18-3-402, or in section 18-3-403 as it existed prior to July 1, 2000, or assault as defined in sections 18-3-202 and 18-3-203.
(3) Notwithstanding the provisions of subsection (1) of this section, a person is not justified in using physical force if:
(a) With intent to cause bodily injury or death to another person, he provokes the use of unlawful physical force by that other person; or
(b) He is the initial aggressor; except that his use of physical force upon another person under the circumstances is justifiable if he withdraws from the encounter and effectively communicates to the other person his intent to do so, but the latter nevertheless continues or threatens the use of unlawful physical force; or
(c) The physical force involved is the product of a combat by agreement not specifically authorized by law.
(4) In a case in which the defendant is not entitled to a jury instruction regarding self-defense as an affirmative defense, the court shall allow the defendant to present evidence, when relevant, that he or she was acting in self-defense. If the defendant presents evidence of self-defense, the court shall instruct the jury with a self-defense law instruction. The court shall instruct the jury that it may consider the evidence of self-defense in determining whether the defendant acted recklessly, with extreme indifference, or in a criminally negligent manner. However, the self-defense law instruction shall not be an affirmative defense instruction and the prosecuting attorney shall not have the burden of disproving self-defense. This section shall not apply to strict liability crimes."
"18-1-704.5. Use of deadly physical force against an intruder.
Statute text
(1) The general assembly hereby recognizes that the citizens of Colorado have a right to expect absolute safety within their own homes.
(2) Notwithstanding the provisions of section 18-1-704, any occupant of a dwelling is justified in using any degree of physical force, including deadly physical force, against another person when that other person has made an unlawful entry into the dwelling, and when the occupant has a reasonable belief that such other person has committed a crime in the dwelling in addition to the uninvited entry, or is committing or intends to commit a crime against a person or property in addition to the uninvited entry, and when the occupant reasonably believes that such other person might use any physical force, no matter how slight, against any occupant.
(3) Any occupant of a dwelling using physical force, including deadly physical force, in accordance with the provisions of subsection (2) of this section shall be immune from criminal prosecution for the use of such force.
(4) Any occupant of a dwelling using physical force, including deadly physical force, in accordance with the provisions of subsection (2) of this section shall be immune from any civil liability for injuries or death resulting from the use of such force.
History
Source: L. 85: Entire section added, p. 662, § 1, effective June 6."
