What should I say to a 25yr old pregnant girl who wandered in where I work this morning?

call the police. they will be better able to know what to do for her. get her in a home and then have the resources to have the child taken from her upon delivery. you can try to convince her all you want, all you're going to end up doing is giving her free food for the day and tonight, she is going right back to doing what she does. call the police.