It's not lying. Your friend's nails are real. She paid for them, she wears them, and you can see them and touch them. They are not imaginary; they are real. If asked 'are her nails real,' the answer is yes, unless you want to start grilling every woman you see about their face lift, tummy tuck, boob job, skin resurfacing, makeup base, blush, eyelashes, (is that your real lip color? because I can tell it's fake) hair pieces, hair color, liposuction, etc., its alllll real. Otherwise you will make yourself miserable clocking every woman who says yes they (whatever it is) are real for anything and everything every woman has ever had done or undone, lifted, sucked, tucked, stuffed, girdled (is that your real stomach? haircolor? brows?), or stuck into or onto her body.
Whether or not you subscribe to her same process of identification, it is neither your business nor your position to gauge what she thinks about her own nails. You can safely, and with conviction, say yes, they are real.