She could have a mild case of chicken pox, it's not that uncommon. Similar to when people get the flu after the flu shot. I don't have any personal experience Varicella (chicken pox) is one of the vaccines we are opting out of, however this is from the CDC page:
Mild Problems
* Soreness or swelling where the shot was given (about 1 out of 5 children and up to 1 out of 3 adolescents and adults)
* Fever (1 person out of 10, or less)
* Mild rash, up to a month after vaccination (1 person out of 20, or less). It is possible for these people to infect other members of their household, but this is extremely rare.
Here is the link to the page, there is a lot of good information on their site: http://www.cdc.gov/vaccines/vac-gen/side-effects.htm#vari...
It sounds like she just has the mild rash, which is actually a mild case of the chicken pox (they don't say that right out because then they would have to give parents a better answer for why we need to get this vaccine- but that's another post!).
What I would watch for is to make sure if you have older family members around (grandma, grandpa etc) they should probably stay clear of the little one for awhile. While rare (per CDC) if she can pass it on to people they could get shingles which is very painful and can get really bad in older people.