The other day she also said "I wish I could just take the baby because you two (me and DH) have no idea what you're doing"
Between this and the equally outrageous "Don't you love your baby" comment, it seems that you need to set some extremely firm boundaries with your MIL in terms of how she speaks to you.
First step is to speak to your DH when she's not there. Tell him you find it grossly insulting and unacceptable to be told neither of you know what you are doing, and to have your love for your child questioned. Your MIL appears to have very little respect for you, and it is stressful and unhealthy to try to maintain a civil relationship with someone who feels they can insult you freely with no consequences.
Let him know that you have decided to set a boundary with her that if she speaks to you in such a degrading way again, you will stop inviting her into your home. Ask if he is going to be prepared to have your back on this, and if not, why not.
If it appears that your husband genuinely thinks it's fine for his mother to insult you both and then carry on with the relationship, ask yourself whether your relationship with him is one you really want to continue in. If he has grown up in an environment where he has been insulted and criticised all his life, he may be inured to it, and not see how wrong it is. Without getting angry with him, you could encourage him to attend couples counselling with you to try to understand why this is a really unhealthy relationship model for him, and also for your child to grow up seeing.
Next step is to contact your MIL and set the boundary. You could do this by email or over the phone, or on territory that you can leave if she becomes insulting. You don't want to have her in your house where she can refuse to leave and cause a stressful scene. She will probably not take it well, and will argue and act like you are being unreasonable. You can simply repeat, "You are entitled to your opinion, but I will not have my parenting insulted or love for my child questioned, so you will need to keep your opinion to yourself if you want us to have a good relationship going forward." If she keeps trying to make it a battle, you can eventually say, "I am sorry you are upset by this but I don't feel there is any value into going over it again. I have let you know where the line is for me, and I hope you can respect it." Then just leave.
She will either haul herself into line because she wants continued access to her grandchild, or she will have a tanty and cut contact, which will give you some peace.