Waaaay too young. The younger the child, or older the adult, the more dangerous it is. Also, at her age, it may be more difficult to explain to her she can't scratch at the sores.
For healthy children, chicken pox is usually more of a nuisance than a real threat. On rare occasions, though, even healthy children can develop serious complications from chicken pox, like a bacterial skin infection, pneumonia, or encephalitis, a swelling of the brain.
If your child has chicken pox, call the doctor if she seems sicker than expected, if she develops a fever after the first few days, if the rash spreads to her eyes, or if the skin around the pox becomes swollen, painful, or very red.
If your toddler has a weakened immune system from a chronic illness such as leukemia or from taking high-dose oral steroids (for asthma, for example), the infection can cause grave complications. Some special protective measures, such as an injection of varicella zoster immune globulin or the varicella vaccine, can only be useful shortly after exposure. If your toddler's immune system is compromised, call her doctor at the first sign of chicken pox — or even if she's only been exposed to someone who's sick.
from here:
http://www.babycenter.com/0_chicken-pox_11416.bc
Also, there is some misinformation in this thread. Shingles IS chicken pox in adults. SO people saying you can't get shingles if you don't get chicken pox is wrong. If you don't get chicken pox as a child, it is very likely you can get shingles as an adult.