My mom has asked me twice if she can come up and stay with me. You'd think after ignoring the…

My mom has asked me twice if she can come up and stay with me. You'd think after ignoring the question she would get the hint that I don't need her up here. It would be my step dad my mom and two little siblings and I have a three bedroom home with three boys my husband and myself then soon to be baby. I don't get along with my mom she as I've said before addicted to drugs and pops pills. I feel like she only wants to be here when I have the baby for the medication that you get after which I don't even get because I don't take it. I wish I could say I want the help but I know she won't be any help but only stress. My bills will go up my husband is the only one working and I just can't do it to him as he doesn't want to leave her here alone in the house and doesn't even trust her when he's not here and working. How do I lightly tell her I don't want her here.