It depends on a lot of factors. For first time petty theft I'd expect she'd be out soon but you'll need to get an attorney involved ASAP to make sure she doesn't spend more time in than she should be doing.
Mr. Feasel is a former prosecutor in San Mateo County (CA) with over 10 years of criminal law experience. Nothing stated on this site shall in anyway be construed as legal advice, or as creating any attorney/client relationship. If you would like to hire Mr. Feasel to further investigate your situation, feel free to contact him thru this site.
Is this a felony or misdemeanor? As a felony the maximum is 3 years. If its a misdemeanor the maximum is 180 days. Felony theft is greater than $950.00 however it is not usually strictly applied. What the punishment is depends upon the strength of the case against your daughter and her record.