Honey, those issues are probably going to be there for your mom when you have a baby totally apart from co-sleeping.
Especially if you have a girl, she is going to see a little vulnerable person and feel strongly like she needs to protect that little person from the harm that she herself suffered. Co-sleeping is probably going to be a "hot spot" for her though.
Here's my advice, since you're asking: you can gently and respectfully suggest to your mom that one way of developing healthy boundaries all around is for your mom to respect the boundaries within your family. Like, you will do what works for you, and your mom can agree (she may need support around maintaining this!) to respect your practices. That in itself is a kind of boundary, do you see?
The main thing that comes up for survivors of sexual abuse is trust. My recommendation (again, since you're asking) is to be upfront in talking about trust as an issue, and gently and patiently requesting that your mom trust you to take care of your child appropriately and responsibly. Remember, your mother didn't get that. She is going to see concerns where others do not, and she may identify strongly with your future child. It may be very difficult for her to disentangle herself from you and from your child (poor boundaries, remember?) Keep honouring and respecting her. You may want to tell her that she is free to say anything to you, and that you will always listen to her.
Keep in mind that co-sleeping is not the issue. The issue is your mom's sense of self was not allowed to develop without negative interference in her family of origin. If you like, you could view this as an opportunity to have your mom get complete about what happened in her family of origin - to transform her experience of families as places of love, trust, respect, and healthy and appropriate nurturing, places in which parents (that would be you, soon) are responsible and accountable for their behaviour.
I'm a little worried that this sounds preachy, but I'm giving it up to you and your mother. Take what you like and leave the rest (as they say at my La Leche League meetings!)