I believe she is guilty of 1st degree murder. As per the jury instructions below by your scenario of culpable negligence (leading to death), being in the phone or the computer and not watching Caylee, followed by failing to call 911 is IMO reckless disregard for human life. Thus, Casey would be guilty of aggravated manslaughter of a child.
I would have accepted a verdict of aggravated manslaughter of a child to avoid a hung jury.
AGGRAVATED MANSLAUGHTER OF A CHILD
§ 782.07, Fla. Stat.
To prove the crime of Aggravated Manslaughter of a Child, the State must prove the following two elements beyond a reasonable doubt:
1. Caylee Marie Anthony is dead.
2. Casey Marie Anthonys act(s) caused the death of Caylee Marie Anthony.
Or
The death of Caylee Marie Anthony was caused by the culpable negligence of Casey Marie Anthony.
I will now define "culpable negligence" for you. Each of us has a duty to act reasonably toward others. If there is a violation of that duty, without any conscious intention to harm, that violation is negligence. But culpable negligence is more than a failure to use ordinary care toward others. In order for negligence to be culpable, it must be gross and flagrant. Culpable negligence is a course of conduct showing reckless disregard of human life, or of the safety of persons exposed to its dangerous effects, or such an entire want of care as to raise a presumption of a conscious indifference to consequences, or which shows wantonness or recklessness, or a grossly careless disregard of the safety and welfare of the public, or such an indifference to the rights of others as is equivalent to an intentional violation of such rights. The negligent act or omission must have been committed with an utter disregard for the safety of others. Culpable negligence is consciously doing an act or following a course of conduct that the defendant must have known, or reasonably should have known, was likely to cause death or great bodily injury.
If you find the defendant guilty of Aggravated Manslaughter of a Child, you must then determine whether the State has further proved beyond a reasonable doubt that Caylee Marie Anthony was a child whose death was caused by the neglect of Casey Marie Anthony, a caregiver. Child means any person under the age of 18 years.
Caregiver means a parent, adult household member, or other person responsible for a childs welfare.
Neglect of a child means:
1. A caregivers failure or omission to provide a child with the care, supervision, and services necessary to maintain a childs physical and mental health, including, but not limited to, food, nutrition, clothing, shelter, supervision, medicine, and medical services that a prudent person would consider essential for the well-being of the child. Repeated conduct or a single incident or omission by a caregiver that results in, or could reasonably be expected to result in, a substantial risk of death of a child may be considered in determining neglect.