I don't have the evidence, of course, but this is the heaviest charge the prosecutor could lay given her decision not to go to a Grand Jury (which is required for Murder 1) and in my opinion it may be a critical mistake. Here's why.
If she thought she has a murder charge (as opposed to manslaughter or felonious assault) she should have gone to the Grand Jury. Then the heat is off her either way; if she gets no bill out of the Grand Jury then it's not on her. If she gets a true bill then again, she's made her presentment.
But the problem with a Murder 2 charge is that if she overcharged -- that is, she basically swung the biggest bat she could and pushed the envelope -- she's got two separate problems. I'll get to those in a minute but before I do some groundwork is necessary.
Murder 2 is defined in the law as killing of another human being during the commission of a felony that is imminently dangerous to human life. Note that the distinction between Murder 1 and 2 is that the person has to be the direct contributor to be charged with Murder 1 -- but not Murder 2. So in this case if you can charge Murder at all since there was no other party involved the only reasonable charge is Murder 1.
(The most-frequent time you see Murder 2 charges is when there's a robbery or some other serious felony and one of the people shoots another -- those not directly involved in the shooting part of the crime but otherwise involved in the predicate felony -- in this case the robbery -- will often be charged with Murder 2.)
That by itself says there is likely a political element in this -- like avoiding "instant riot -- just add New Black Panthers" (who, incidentally, the government has refused to arrest despite what appear to be clear violations of the law in their advocacy all on its own.)
So now on to the problems:
•The jury may refuse to convict. Remember that the standard is proof beyond a reasonable doubt. Not "I think he did it", not "more likely than not." And it's considerably easier to prove manslaughter or felonious assault than it is murder, especially when Murder 2 is the charge to use when your felony contributes to, but is not the actual cause of, the death of the other person -- and clearly, Zimmerman was the one who shot Martin.
•Because of Florida's 10/20/Life Law, a murder charge is (mostly) a no-op in this sort of situation anyway. A Murder 2 charge carries a term of any number of years up to life; capital punishment is precluded, and there is no automatic number of years. This is compared against Murder 1 which has only two possible penalties -- life in prison and the death penalty. The problem here is that Florida's 10/20/Life says that if you shoot someone in the commission of a felony you must be sentenced to at least 25 years additive to whatever the predicate felony sentence is and you must serve every day, with no early release or parole. So if Zimmerman is convicted of Murder 2 and given a 20 year sentence, for example, he must serve at least approximately 35 years -- 25 on the firearm where there is no credit available and then, and only then, sequentially on the predicate (for which the usual credit can apply.)
From a standpoint of punishment there is scant difference between manslaughter and murder 2 in this instance. The reason is the mandatory sentence for the shooting -- that 25 years is a "serve every day" sentence and comes first. As a consequence the penalty for manslaughter (15 years maximum) is not much different to a 30 year old man because you have 25 you must serve straight-up first.
In other words even if Zimmerman was to draw zero on a manslaughter conviction (ha!) he still does 25 years, which makes him 55. If he does 10 more for the manslaughter he's 65 before he gets out. And the difference between 65 and 75 is both not much and puts you into the range where the odds are high you're going to die in prison either way.
In short Murder 2, in my opinion, was unwise. It greatly increases the risk of an acquittal, it leads to too many questions about whether the charge was political rather than fact-based as if the facts supported a murder charge she should have gone to the Grand Jury for the capital offense as Zimmerman was clearly the one who did the shooting, the effective sentence for both manslaughter and murder in this case is functionally close to identical given Zimmerman's age and if the jury believes there is any sort of taint in the process they are very likely to refuse to convict -- which is their job.