The simpliest solution is the best. tell your girlfriend she has a smelly pussy, and you wont have physical contact untill she cleans it.
She cleans it.. but she spends a day at my house, then we spend a day at her house.. and there the shit is in the door welcoming us when we walk in..
Which brings me to another smelly pussy story..
When we had only been dating one month, she told me that in the vacant lot next to her living room window, a stray cat had died. She tried contacting the owner but they got no response. She then tried contacting the city hall to see if they would clean it up, and as you might guess, they don't get up off their fat asses ever.
She tried the owner again, but no dice..
I must add that she's a squeemish girl who loves cats, and she wasn't capable of cleaning up a dead stray cat. By this time the cat really started to smell and the stench was permeating the house and she was having company that night. I (reluctantly) volunteered to remove the dead cat.. It was horrible!! I jumped out the window with some bags, picked the damn thing up and a 6in diameter ball of maggots fell out!
I happened to have my camera in my pocket and snapped a quick one to share with you all nice folks:

I almost threw up!! If I had been thinking clearer, I would have made a video because you could see all the maggots wiggling.
I eventually bagged the cat and it went to a dumpster and I re-evaluated my love for this girl. She passed the test, but we still have smelly pussy problems.
Kill the cat with mercury. buy a few glass thermometers, and put the mercury in an eyedroopr. when the cat is asleep and your girlfriend isnt looking, drop a drop on its back. the mercury will seep through its skin, and after a few weeks of doing this, it will die.
I think the risk is too high. I'd have to do it repeated times while she is home. And if I got caught, how would I explain the eyedropper with mercury in it?