I think Lauren's card means Beale's home - after all, that appears to be what she told Peter, that Lucy was killed in their home, hence him going off at Ian and Jane.
Puzzlers though...
If Peter, why would he confront Ian and Jane?
If Cindy and any of the Beale family knew it and helped cover it up, what would be the point of the music box at Christmas?
If Abi, then wouldn't Lauren's reaction be a bit different? Loved, not "cared".
If Max, then same applies as with Lauren.
So... possibility that Lauren doesn't have it quite right?
If Bobby, I think the police officer's response would be much different - surely she'd be more concerned about where he was and the texting wouldn't make much sense, unless it was Jane texting back and forth with her.
But then, Lauren seems cagey, so I could see that if she thought Peter either killed Lucy or was involved, she might not be able to have his baby (in her mind, anyway). So there is that thought too.
Yup. Full circle. Still could be anyone. 