The only way you know for sure that she is ready to harvest is by checking your trichs under the scope. You can get one cheap, 30x or more magnification, at Radio Shack, or a comparable store.
You want all the crystals to be at least cloudy, all clear gone. The more amber you see in the crystals the more of a body stone, the less amber or just cloudy, more in the head.
How many days has this plant been in flower? If it's less than 50 I would strongly doubt she's ready. There are other physical signs you can use, like if at least 60% of the hairs have changed color, or the leaves are starting to die off, but really, without a scope, you can't be sure.
If you're less than 50 days take a nugget and let it dry naturally for a couple of days, toke it, if you like it, harvest the tops, drop the light or raise the chopped plant as tall as your others, and let the bottoms finish for another week.
Good luck