Collect addresses for her, let her use your home as a contact point, if she wants to set up an escape fund could she use your address for paperwork.
set up a code between you so if she feels in danger she can phone you, no suspicion that way and you call police. maybe asking if you have a book she can borrow or did the little one leave a toy at your place.
Just be consistent in telling her finances are no use it be kills her then what will happen to her child.
And most important Don't let her other half know you think differently about him, if he guesses she has told you it will just prompt another attack and if he feels threatened he may force a move away.