Hi, Brittany,
I'm SO sorry about what happened to your mother, and to you and the rest of your family and the people who cared about her. I hope you've gotten some help in dealing with the incredible pain that your mother's murder must have caused.
I can't tell you what is happening specifically with your mother; there may be others here who can. In my experience (and I hope that this is not too upsetting to you), people who die suddenly and violently may have trouble understanding what happened to them, and have a hard time leaving the place where they died, and the people they love.
Please understand, again, that I can't know where your mother's spirit is, or answer with any certainty your questions. But my gut feeling, based on the experiences I've had with the spirits of people who have died unexpectedly, is that they need someone to let them know that they understand what happened, and to tell them that they love and care about them and will be happy knowing that they will be passing on to another place where they can have peace.
My suggestion--and it's only a suggestion--is that you "talk" to your mother, even if you can't see or hear her. Tell her that you love her and miss her, tell her gently what happened and what's transpired since (for example, if your stepfather has been prosecuted, or anything else that's relevant), and tell her that you want her to get to a place where she can find peace and perhaps still watch over you and your baby (and definitely tell her details about your baby that will make her happy!

). I don't know if you're at all religious, or ascribe to any faith, but what I do when I encounter "lost souls" is pray for them to whomever might be listening, and explain who they are and the circumstances of their death, and ask that they get help in getting to "the light", or wherever it is that spirits go to find peace and help. I don't know who, exactly, is listening, but I feel very sure that someone is, and that your mother will be cared for. I also feel that it will help her to hear directly from you about the things she would care about.
I hope that helps. Again, I'm very sorry for your painful loss. I do believe that your mother will hear you if you speak to her (I don't think that you need to do it out loud, necessarily--just find a quiet place where you can talk to her in your head, or, if it feels more helpful, in a whisper).
Feel free to write again.
Doe