Ahh love the freeman of the land rubbish. The Communications Act 2003 requires you to have a tv licence if you watch tv etc etc. It's not a contract, it's not a "I don't feel like paying today", it's the law that government has set
Her argument could be the same for road tax or insurance. Road tax is a contract with the DVLA therefore I don't feel like entering the contract today and as such will not be paying for it. I will, however, continue driving on the roads. Again, legislation states you have to have road tax to go on the road.
Regardless, an act of parliament aka the Communications Act 2003 is law. Regardless of whether you agree to it or (ie: whether you consent to it or not) is neither here nor there. Parliament act on our behalf after we, the public, vote them in. Therefore, we give them a mandate to act on our behalf.
SO, the gf needs to pay.
Those people who opt out of things, who then complain of police harassment, actually have no leg to stand on as harassment is a concept introduced under the harass act. Something, as an act, they don't believe in.
Anyway, I digress. If she doesn't want to pay, await her court summons!