Is there fullproof way to get someone high for the first time?

[C.R.E.A.M.]

You could always give her a brownie, or use one of the ideas in the recipe forum. If you give her a brownie she will surely get high, but her lungs will still remain untouched. I'm not sure if your motives are to get her high, or for her to become a regular pot smoker, so I can't pinpoint what exactly you want for her.