Using opaque powders to mask the natural nail (custom blending) really does require some practice. If you can't get enough practice in before having this client in and don't feel confident with mixing a correct coverage color, I would suggest doing what I did before I start custom blending:
Sculpting (or perhaps using clear tips and then creating your own smile line on top) really would be the best thing. And you are the professional, you have to make this clear to the client. After extending the nail bed with your regular clear or pink that you use for Pink and Whites (do a search on here about nail biters and custom blending, you'll find how to saddle a tip if you choose to extend with clear tips, or you'll find how to apply forms to a bitten nail and then extend on top of this), use a sheer pink polish to disguise the natural nail that will be obvious in zone 2. My favorite for this is Sheer Contentment by CND. It is a shimmery gold/pink that covers the natural nail, but does not turn your whites pink. Here's an example of how I sculpted with sheer pink and used just one coat of Sheer Contentment.
Before:
http://img.photobucket.com/albums/v225/buttpaste/Salon Stuff/Nails/100_2366.jpg
After:
http://img.photobucket.com/albums/v225/buttpaste/Salon Stuff/Nails/100_2368.jpg
You can still see where her natural nail was slightly, but if you don't have enough time to practice custom blending, it's still a much better result than sticking white tips way down on a nail bite, in my opinion. Hope this helps.