First -- I'm so sorry. You love her and you also want to LIKE her but you cannot. It is possible to have someone whom we love but cannot like, and whom we love but who is simply bad for us to be around.
Care for yourself first and foremost. You say you're fighting depression. Are you in therapy? If you are not in therapy please get into it -- now. If you feel you can't afford therapy, run, don't walk, to your city or county health department and find out about sliding scale fees for mental health help; also get to your local "women's center" (look online for these), which is a free resource center that should be able to help you find some low-cost therapy. You need professional help to deal with a lifetime of being put down and belittled. Don't try to fix this on your own! Is your husband supportive of your getting help? I hope so - you need support at home. And he and you both need to see that therapy makes you a better wife and mom because only if you are healthy can you be at your best for your family.
(If you ARE already in therapy -- are you being really open with the therapist about what you say here? The therapist should be giving you ways to deal with mom.)
Next: Say this about a thousand times: "I cannot change HER. I can only control my own reactions to her." This is easy to say but so hard to do, but try to embrace it. (Again, therapy should help with this.)
She is one of those people who, sadly, truly believe they are "honest, open, frank, all about truth-telling" and others are "hiding, denying, unable to handle the truth." I know folks like this.These kinds of personalities honestly think they are in the right and are upstanding, brave and honest, and actually helping others by criticizing them, and those who are hurt by them are weak and unwilling to improve themselves. In reality, they are making themselves feel better by belitting others.
Realize that this is a fundamental, unchangeable part of her personality (at least, unchangeable without tons of therapy) and is NOT about you at all. Again, therapy would help you cope with this fact and would give you some coping mechanisms to use whenever she criticizes.
Meanwhile, either stop seeing her, or if you feel you must see her, see her less. Limit the contact. She WILL complain and criticize about that too so be prepared for it and do not cave or let it get to you. If you just announce, "You're toxic so I'm seeing you once a month" she's going to go nuts on you, so don't bother; just tell her you can't see her this week but will see her next week. No explanations, no excuses, a big smile in your voice and don't answer questions: "I can't make it but I'll see you next Thursday at X."
I like what someone else posted about walking out when she criticizes. Tell her that you want to talk about your kid's latest cute saying or whatever but not about your appearance, marriage, choices. When she starts, pick up your keys and say, "I need to go now. See you later" and don't engage in anything else.
When you do see her, don't just "visit" and chat at her house - that's her turf - or your house, which gives her an opening to look around and find something she must criticize. It can help to do something together outside either home, so you can focus on the activity and can redirect her focus to the activity. She's going to slip and keep on criticizing but if you have something to look at or do, you can keep your focus on that. Keep it short, too. Maybe meet her at the mall bookstore, tell her you both can browse together, and tell her you need to leave in an hour and then stick to that time.
Again, all that is only IF you really need to see her. I would get into therapy quickly and see what a therapist says about whether or not to see her. You might need to get stronger first, or to break off contact for a while.
That leads to one last thing - you say "she is the only parent I have, my best friend." Please think hard about that statement. She is your parent but that does not mean she is a good parent or a kind person, and you do not owe her your attention; she has lost her right to that through her treatment of you.
And as for being your best friend -- no, she isn't a friend. No real friend treats a friend the way she treats you. Ask yourself: If she were not my mom but a woman friend, would I tolerate her constantly putting down me and every aspect of my life? I hope the answer is no. One aspect of healing would be to get out and find adult women friends of your own, who know you as you are right now, who have no baggage of having raised you, and who will not treat you this way.