Jeez, that is too much work and too painful.
Just tell her, "Sorry, I can't make it. Something came up."
Honesty is the best policy.
On the other hand, if you really want to get sick just for kicks because you are feeling masochistic today - well, hell, everyone had a lot of - interesting - ideas.
But I find the best way to get sick depends on the individual. I bet some people can drink turpentine without bothering them; others drink a glass of milk, and they are shitting all day.
Although I've never tried to get sick, I notice that if I am in a rush and leave the house without drying my hair when it's really cold outside and don't dress warmly enough, I will get a cold, sure 's shootin'. But that's just me. And my colds go directly to my throat, so I can't talk for shit.
Now I don't do that anymore because I noticed the pattern and stopped the behavior.
That's a start.