Ok this is a big mess and long story so for those of you that read it all thanks.
My younger sister just moved back in with me with her 9 month old daughter.

It started that she met this guy and got pregnant. They were going to get married and then things started getting really bad so she left him. Well after the baby was born he pursued her to come back because he wanted to be a family. My sister is young she is only 20 and so she gave up everything she had been working for and went back to him. His grandmother takes total care of him pays his bills sends him money constantly. He has so major issues especially with money. While my sister was with him the first time they got 20,000 in credit card debt. She had perfect credit and he has awful so he talked her into getting all these cards telling her how they would be paid once he finishes pilot school. Sorry got off track there...
And once she went back to him he talked her into getting married after 2 weeks of living with him. Then he told her if they moved to California everything would be great. He is originally from CA; we live in FL by the way. His grandma was going to buy her a car so she could work and he would go to school and finish. Well once she got there it was awful. He was totally controlling. His mom is crazy... I mean there are court records showing this but everything she said was golden to him. His whole family talking awful to her. She was just living in the apartment with the baby while he went to school and worked a few hours a week. He recently even had a breakdown where he went into the bedroom screaming hitting walls and wouldn't calm down for hours. This is when she decided she needed to get out of there and return to Florida. They hadn't even lived 3 months in CA and she does not know anybody there, no family there, no job, no nothing.
So we paid her airline ticket and she is now temporary living with us back here in FL. She did not tell him she was coming to stay, but rather made him think she was going for a 1 week visit when she fly to FL, because he had already threatened her that he would not let her leave with the baby.
It's not that she don't want the dad to see the baby that's why she went back in the first place it's that she down feel that she is in a great situation there. She said the dad will throw things at the baby and knock her over and then laugh about it. Just does crazy things that shouldn't be done with a baby... he has never hit her or the baby... yet
We don't know where to go from here though. To file for divorce in Florida you have to live here for 6 months... to file in California you have to live there for 6 months... she only lived in California 2.5 months. So we are stuck in a situation and we don't know what to do. He is of course making all the threats he can now to get her back there. He even admitted he didn't care if she was happy because he was and that's what matters. I have never seen anything like this in my life. So any advice would be greatly appreciated. We want to make sure its legal that she took the baby and came here? She is not expecting anything from the father money wise because he gets all his money from his 74 yr old grandmother. She don't care if he comes to visit the baby she just wants away from there and that crazy family. So please help with any advice you can... A little more information. My sister lived here in Florida for 2 years before moving to California for 2.5 months. Ok sorry this is so long just any advice is or knowledge on the situation is greatly appreciated.

Obviously she needs to talk to a lawyer & many give free consultations.

Most of all she needs to document any abusive behavior & all threats. She has to do that in order to protect herself & the baby legally especially if he gets even worse, which he's likely to do when he sees he's not going to get what he wants from her.

I'm not exactly sure where she was living prior to being in Calif, was that Fla? Her moving to Calif for such period may not have invalidated her residency where she lived before, so if that was Fla. She can still file for divorce sooner than waiting the full 6 months but I'm not a lawyer. It might be considered as an extended vacation to see if she wanted to make a permanent home in Calif but decided not to, at least that's a possible argument that could be made if she filed immediately (assuming a Fla residency before Calif). Did she change her driver's license to a Calif one?

I would suggest she talk to the local battered women's shelter. They are used to dealing with situations like your sister's & may have free legal advice available to her there. They will tell her what she needs to do in order to protect herself & the baby.

DivorceNet - Divorce Checklist and FAQ's

If I am a Florida resident but temporarily reside out of state, can I still consider myself a resident for purposes of getting a divorce?

That issue will be up to the Court, but if the Judge decides that you are truly a Florida resident, who is for example working for a corporation outside the state, or visiting elsewhere for a short period, etc. you will probably still be considered a Florida resident and can get a divorce. On the other hand, if the Court determines that you really have no intention of coming back, or that you realistically are permanently living elsewhere, even though you may travel back and forth to Florida from time to time, you probably will not be considered a Florida resident. Also, if you are in the military, the fact that you are stationed outside of Florida does not detract from your Florida residency.

What if my spouse is violent or harasses me?

In an extreme situation of course, the police must be called. Aside from that, in Florida there is a procedure for getting a restraining order if your spouse is guilty of certain conduct, without notifying your spouse of your efforts to get one. (consult the clerk of court or a lawyer) If the Court does issue a restraining order on this basis ("ex parte") there will be a hearing within a number of days after issuance of the restraining order where your spouse can come in to Court and defend himself or herself. This procedure can be used even before the divorce process begins. Once the divorce process begins, the Court can order your spouse out of the house if things are bad enough (especially where children are involved) as well as order your spouse to stay away from you. These matters have priority in the Court system and do not have to wait until the absolute end of the case. Under no circumstances should you make false claims against your spouse in order to gain advantage in your pending or anticipate divorce action!

Can the Court order something different than shared parental responsibility if my spouse is a danger to the child?

Yes. If the Court finds that it would be detrimental to the child for the noncustodial parent to participate in decisions concerning the child, then the other spouse can be given sole parental responsibility.