Either bad lawyers that couldn't convince the judge that she was acting in self defense, or the judge saw evidences that she wasn't acting in self defense. The reason she's got so many years is because she's been convicted of attempted murder and there's a mandatory minimum sentencing (which is extremely dumb, by the way).
This woman gambled and lost big time. She rejected a 3-year sentence plea deal knowing that if she'd lose, she'd get 20 years.
It's not because she's black.
It makes no sense. Her mistake was to return to the house, and that stopped the case being a self defence under "stand your ground". However, Zimmerman did the same, so surely he too lost the defence of "stand your ground" as he went on the offensive.
When she went back, she only wanted to force her abusive husband out of her own home by making him fear for his safety. Of course, she should have dialled 911 and got the police to deal with the matter, but so should have Zimmerman.
Surely there is as much doubt over what exactly took place in both cases, so it appears she got convicted unfairly of an offense far more serious that the one she committed.
Also, in the Zimmerman case, surely the victim could also have argued "stand your ground" when he was made afraid by this person getting out of their unlit car to follow. The "stand your ground" law would allow him to confront, rather than flee. Someone parked up in an unlit car is not exactly just "going about their normal business", and if you see them get out and follow you, surely it is not unreasonable to feel fear for your own safety. He attacked Zimmerman first, but this too is surely covered under "stand your ground". Neither party could know what the agenda of the other was, and this is the bigger problem. Effectively, this law created a situation where each party could use deadly force under the "stand your ground" law, and only one outcome was possible, one dead, and one found not guilty.
I am also surprised at someone with that past record (Zimmerman) being allowed such a position in the first place. The UK have closed a similar loophole in our own private security industry by bringing in a licensing scheme, and banning those with a history of violence and serious crime from working in "security".
It seems the US "right to bear arms" makes the consequences of such mistakes all the more serious. Here in the UK, it would at worst have been a beating and/or forcible detention whilst awaiting the police, rather than being shot dead. We do have armed police, but they attend only as back up when there are grounds to believe a firearm might be used in a crime or attempt to escape. They have also been known to make serious mistakes.
Maybe "stand your ground" needs to be restricted, perhaps to incidents where a trespass has been committed, such as someone entering your home uninvited. There have been calls in the UK for some kind of right to use force in situations where your place of safety has been violated without having to worry about what would be deemed "reasonable" in a legal sense. There is already a "reasonable force" defence, but this is lost as soon as someone pursues an offender once they start to run away. If in the home, you could also lose the defence if you deliberately block their exit and force a confrontation.
As for Marissa Alexander, she should appeal and get a better legal team.
. I was stopped about 5 years back for that. You should come for a ride along one day. Yes yes my motives are pure.....mostly....well they started off pure 
