Your mom sounds lonely. However, that can be remedied by keeping in touch with the children that she has now - all of them.
Your mother's local CWS agency will run a thorough background check, before they even consider placing a child with her. Plus, they do take into account such things as the age of the foster parent, and multiple pet replacements within a given time period. If you feel that she is really going through with this, a word to the CWS agency would not be amiss. You can explain the situation to them, and request that they list you as "Anonymous" in her paperwork.
I realize that this is a sensitive topic, and if I've written anything that makes you uncomfortable, I do apologize. IMHO, it just doesn't make any sense to take on the responsibility of fostering other people's children, while refusing to deal with the ones that you yourself have brought into the world. Plus, we don't need any more children abused by the Society's teachings.