I've been there. I moved to another state, 12 hours away. I know what it's like to be homesick and it's hard enough without a baby. There are times when you feel that you need your mom and nobody else will do. She's got nobody here, except for your brother and the baby. Sorry hun, your family doesn't qualify quite yet.
I agree that moving back home and nobody having a job isn't the best laid plan, but be glad she wants your brother to go with her. She still wants her 'new' family, but she needs her own at the same time. Since she's not working now, she can take the baby and spend some quality time with her family and friends. If she does and decides she just doesn't want to stay here, then it might be worth moving "home".
I know my husband would have been willing to give up his job, apt. etc. and move to Kansas just to be with me. If I had asked him to, even still today after he's finially got a foot in the door at his dream employment location he'd still pack up and move. Keep in mind his family is here and if we moved back to KS, we'd have nowhere to live *except with family* and no job.
I would focus on being her friend, helping with baby/around the house anything to make her life less stressful. You can let her know that you know it must be hard being so far from family and friends. But from what you've been led to believe, it gets easier when you've made new friends and let others be part of 'you/your family'.
There is nothing you can, or should try to do to change her mind. All you can do is help her enjoy her time here. Most of all, if you're a parent you know it's not easy. You also know it's not easy leaving your little ones with people you haven't known long enough to call family.