Do you have adult children? I need advice.

[Swan]

Yep! Sorry for the lack of replies. I've been job hunting and catching up with some friends who popped in from out-of-country to visit.
The "no locks" law is my dad's, and he has some solid reasons for it, so I respect that. It's getting mom to quit barging in without breaking my dad's rule that's the issue. She's been a little better these past few days (whew... finally a relief), but I'm sure she'll be back at it again soon. Are there any tips on how I can go about talking to her in a way she'd listen to without twisting it in the interim between now and when I can move out, whenever that may be? I noted a few of your replies and agree with the "address the major issues and let the rest lie" bit.

[shootingstar]

If possible always find opportunity to talk about things that you know both of you share a positive interest. And to compliment her when it's deserving. Seek her advice in areas where clearly she has expertise/knowledge.

I don't know your mother so hard to suggest much here.

Just to give an example, my mother can be tough to deal with. (And it will get tougher when my father dies. His cancer is getting worse..)
She and her daughters sew, so it is one area she clearly taught us, has expertise, we asked for her help (especially when we botched some sewing projects) and we appreciate whatever she does in this area. She also cooks healthy for herself and family. It is also an area that she deserves our appreciation because she passed on lifelong knowledge/skills to us that we all have and continue to practice ---naturally.

My mother genuinely likes Mother's Day appreciation for her: she needs appreciation as a mother for her hard work for raising 6 children. I can't dispute this one, for sure! So she likes the card, etc.
I know this doesn't solve her other issues but for the time being, at least she needs to clearly understand you are not rejecting her completely, only certain facets of her behaviour to you are no longer acceptable as an adult.

[nuliajuk]

...The "no locks" law is my dad's, and he has some solid reasons for it, so I respect that. It's getting mom to quit barging in without breaking my dad's rule that's the issue...

You may have to break your dad's rule. If he complains, tell him he can switch back after you move out. Tell him in no uncertain terms that you can't tolerate this behaviour any longer, you might get him on your side or you might not. At least you'll have tried.
My mother also had no sense of boundaries. She'd come over to my first apartment without asking, wander into the bedroom and start rummaging through my closet, make snide remarks about my housekeeping (her house was a tip, but of course that was because "I have all these people to clean up after"). We've been estranged for decades (her idea) and I'm sadder about the fact that I don't really miss her than I am about the estrangement.

[MMEZ]

Perhaps instead of getting locks for the doors, you can get those little wedges that people use to keep doors open. Instead of keeping the door open, use the wedge on your side when you are inside. The door won't have a lock on it, but it will be very difficult to open from outside.

Sorry you are having to deal with this. Your mother sounds quite toxic. I disassociated from my parents about 6-8 months ago. Good luck and I hope things improve soon!