What legal aid will do depends upon the state, as does whether a common law marriage is recognized. Child support will be awarded regardless of whether the couple was legally married or just lived together.
If there is abuse, the clerk of court and/or the police may have court-approved forms that can be filled out and submitted at little or no costs so she can seek protection.
There are way too many variables to say for sure how much someone would make. If you start out with a firm, well, it would depend on the size of the firm. If it's a small firm, maybe as low as $55,000, maybe as high as, well, who knows, $100,000??? depending on how good a law school you went to and how good your grades were. If you go to a large firm, you might start as low as, say, $60,000, or you could start out in the low 100s. Depends on the firm and how badly they want you.
I just interviewed with a large public defender's office in a large city, and the starting pay there was $55,000. If I had been more experienced, I would presumably have been offered more... maybe an extra $5K for every couple of years of experience.
You could go out on your own, in which case your income could be zip, and it could be half a million, depending on about a bazillion things - how well you market yourself, how much people are willing to pay you, whether anyone would trust you, being right out of law school, to handle their case... endless variables. You may actually end up in the hole after you figure in costs to open and run your practice, etc. Not to mention your malpractice insurance. I worked for a criminal defense attorney who had been in private practice for probably 20 years. My totally rough guess is that he made about $200K a year.