I am yet to see a chastity device for girl that is both secure and descreet and comfortable enough for all-time wear even outside the house. A shame, really, but it seems that keeping girls chaste is much harder, than doing that to the boys.

You can't restrain acess to the clitoris and vagina with a small and descreet devise. For one thing, there's no attachment points. Mens genitalia can hold the chastity device right on itself, but for women the closest thing you can secure a device on is waist. Moreover you cant block off female naughty parts without blocking off urethra, which leaves really no options other than massive overhanging cage-type thing above all crotch area, which is, if you look at it, will get really messy after first toilet visit, because you can't clean it properly inside. Mens chastity cages, on the other hand, can be worn, can be secure, and at the same time keep the Urethra opened and not blocked by anything.
Also I can imagine that for some (or even all) women the device would have to be taken off during the menstruation periods for obvious reasons.
So, until someone invents something really devious, I can assume the female chastity are more like roleplay toys.
I can speculate, however, that for the most hardcore and desperate of experiencing female chasisy couples there can be made a device using catether for the urine output (insertable tube), thus keeping the device tight small and descreet enough. However it's probably really unsafe for health, but that's the only real option I can think of.
Here's a blog you might be interested in:
http://lockedlali.com/tag/female-chastity/
And one more, that prooves that with great determination all's possible:
http://www.daisy.co.uk/sites/VannaVechian/femchasv.htm