If your workplace is large enough, maybe they could sponsor a workshop on domestic violence at which she wouldn't feel singled out.Also, see if the local shelter or police have any pamphlets which you could leave around the office, in the coffee area or even give to her, if you feel it appropriate. The pamphlets should explain what abuse is and what resources are available if and when she recognises what is going on and is ready to try getting out. With luck, there will be information on a "safe" house where she could go at a moment's notice.
As the three of you continue to have lunch, etc., perhaps the one with the experience could casually talk about her former days and what gave her the courage to get away.
These are all just suggestions; I have no idea if they would work in this particular situation.
Encourage her independence: does she have her own checking acct.? Her own ATM? Talk in general about how important it is to women, and their children, to have the security of independence.
Here are some websites which may help you and/or her, when she is ready:
Good luck and good for you for being a caring friend. Please keep us posted and PM, if you'd like. I did a series of articles on this, in Wyoming, a few years back, with extensive research. It is not an easy thing.
kat