OP,
It seems to me from what I've read that you put a TONNE of pressure on yourself to make sure that this first kiss is absolutely flawless, perfectly timed, etc. (Which is likely the reason it hasn't happened yet).
It might be advisable in your situation to just go for it the next time you feel the urge to... Has it ever happened that she's said something sweet, or smart, made a great joke, etc, and you've felt an immediate desire to kiss her? If so, I would make a promise to myself (If I were in your shoes) to give in to that feeling the very next time I had it. With over-thinking the scenario, timing, quality, as well as the multiple potential conclusions (her parents seeing, your friend seeing, etc) you will just continue to build up the anxiety, as well as your expectations.
It's very reassuring to hear that you two have been together for the time you have, and that she doesn't equate your lack of physical affection with a lack of interest/care. And all the better to help take some of this anxiety away for you. Would be more difficult, I believe, if you had reason to feel a sense of urgency, in addition to the amount of panic (?) you seem to already have over the situation.
If it helps at all to hear it, my one very good friend admitted to me that the first kiss between her and her husband was less than ideal for her. But she loved him, wanted to spend her life with him, and knew that kissing is very malleable part of the whole relationship equation. Given time (and helpful, gentle suggestions), her husband would one day kiss her just the way she always wanted. People cannot be replaced, and if this girl has been happy with you for an extended amount of time without a kiss, I don't think that even the sloppiest of smooches could send her a-runnin'. Sure, you would likely feel embarrassment if she reacted negatively (in your opinion), but so long as you could be willing to receive/consider constructive criticism, there would be no reason to avoid her!
Besides... For all you know, the way that it occurs to you to kiss someone may be the very way she wants to be kissed, and it could be perfect! You'll never know if you never try, and I doubt you'll try if you keep obsessing over so many details. Try to just let it happen, if you can. It's supposed to just be natural, anyway!