Electra, of course the thought of someone taking your baby away makes you feel angry! It must be the most unnatural thing to have to go through in the world! How can it not affect the mother's, and the baby's mental and physical health?!
It sounds like you have been very strong and determined in beating your mental health problems and making things better for your daughters. I'm sure you will have learnt things from that experience that will help you if things get difficult again. You also proved to yourself that you can survive it. And you've done this without your children's father! I find it hard to cope with my two even though I do have DH at home!
It sounds like your mother's reactions are clouded by her worry about how hard it will be for you, just when it seemed like you were feeling better after going through a hard time, and the thought of it being hard work helping you. She is focussing so much on that and 'solutions' to that, that she can't see at the moment that there would be BIG problems with the alternative of giving your baby away.
I think that before people have had personal experience of adoption they think it isn't that bad a thing for everyone. They see it as, the mother feels she can't cope so she can give the baby to someone who can cope who is desperate for a baby but can't have one naturally, which seems like a kind thing to do for the adoptive parents, and seems like the child will have a good life with people more able to cope, either emotionally, financially, physically or all of those things. With a lot of things it is hard to know how it feels until you go through it. In reality it is more complex than people think and has more effect on the people involved than people think.
I believe that giving your baby away would affect your mental health very badly, and would affect you more than going through the hard work of bringing up another child. It would also affect your baby badly. I could be right or wrong but I'm basing this view on my own experience of being adopted and also how it seems to have affected my birthmother. It is not an easy option. I have struggled with feelings of unworthiness and unimportance and low self esteem and the feeling that I'm searching and searching for something that is missing and never finding it (even though I've met my birthparents). This searching for something that feels missing can make people turn to behaviours that are excessive/damaging/addictive. I feel loss and vulnerability and anxiety and feel I want to be mothered as though I were a child, but the opportunity for this has passed and now I'm an adult I can't have that. I find it hard to trust people and have found it very hard to form friendships in the past and I believe it goes back to feeling abandoned by the person you are naturally programmed to depend on (your mother) when you are your most vulnerable (newborn). This is hard for people to understand because, logically, you can't remember how you felt as a newborn. But so many adopted people say similar things! I believe being taken from your mother damages your instinct to trust and bond with people and you develop an instinct to distrust and to try to be independent and make sure you can look after yourself on your own in case you get abandoned again. The books call it attachment disorder and it is well documented if you feel like looking it up on the net. Adopted children are often resistant to bonding with their adoptive parents and those relationships can become difficult. I don't have a good relationship with mine, which might make my reaction to these sort of threads stronger, but I know that lots of people do have good relationships with adoptive parents as well. I have still seen people who had very good adoptive parents having emotional problems because of the adoption though.
My birthmother went through such emotional pain by doing what she did and because she couldn't face another loss like that she shut down her emotions and shut off a bit from people and kept a distance (if you don't bond, you can't have that bond broken and go through that pain). It has affected her relationships with other people, including her son in my opinion, ever since. She went through guilt and shame and pushed and pushed herself in her career and everything she did, but much too much until it made her ill. I believe this was an attempt to really feel she had made something of herself to distract her from feeling rubbish for what she did. I have met up with her and known her several years now but our relationship is too difficult to be 'good'.
Sorry, I won't 'vent' this anymore because we should be helping you on this thread. But if there is anything in there that would help your mother to see that giving away your baby wouldn't necessarily make everything ok then you can use me and my birthmother as an example for her if you want.
Could you say to your mother something like - I can see why you are concerned about what effect having another child could have on me, my children, and you, but asking me to give my baby away is asking me to do something that would cause me great pain and is likely to affect my mental health and the baby's mental health more than if I keep the baby. It upsets me a lot that you want me to do this and would mean a lot if you would support me in having my baby. I can see that you are worried about how much hard work it could mean for you in helping me, but I am not going to pressure you to help me, you are free to help me as much or as little as you feel happy with. I can also get help from x, y, z etc.
It sounds like you want to keep your mother in your life rather than saying something like Fck off Bitch like some people are kind of suggesting (and was my first instinctive reaction when I read your post), so I wish you luck with taking a more 'moderate' approach and talking to her and getting her to understand your point of view. If she completely refuses to look at things from your side then she is indeed a toxic btch!