Hi somecallmenick
Your anxiety and uneasiness is quite understandable with the prospect of having your mother back around in your mind. It migth help to take a look at some information we have on here about boundaries. This might help you as you try to set and enforce boundaries with your mother:
Getting Our Values and Boundaries in OrderExamples of boundariesVarious communication techniques are described on this website that I think can be helpful to you. Are you familiar with the S.E.T. technique? The acronym S.E.T. stands for Support, Empathy and Truth. The technique helps you to express your truth while minimizing the chance of (further) conflict and maximizing the chance of getting through to the other person. You can read more about it here:
S.E.T. - Support, Empathy and TruthYou mention 'guilt' a few times in your post. Guilt is something that can keep us 'trapped' in situations we don't really want to be in. That's also true for 'fear' and 'obligation'. Are you familiar with the concept of 'FOG'? FOG is an acronym for Fear, Obligation and Guilt.
... .fear, obligation or guilt ("FOG" are the transactional dynamics at play between the controller and the person being controlled.
We have an article here about 'FOG' that I think you might find insightful:
Emotional Blackmail: Fear, Obligation and Guilt (FOG)In the article several tips are given to help you get out of the 'FOG':
In the simplest sense, to change this dynamic we need to alter the way we respond to it.
Step One  :)on’t respond the moment a demand is made. Give yourself time to think and assess the matter. We want to respond - not react.
Step Two Let go of your emotional ties to being controlled, at least briefly, and try to be an independent observer. Gather the information you need to construct a wise response - one that is neither enabling nor confrontational. Likely there is a long history of bad, demanding behavior and enabling responses / resentment, so this is going to take some discipline not to be triggered or to overreact. You may want to enlist a confidant - someone you respect for their emotional maturity and ability to read others - to act as a sounding board. Remember, it's problem resolution, relationship retraining - not a battle.
Focus on the demand at hand, not all the past history. Assess how significant a particular demand is. Remember that there are different levels of demands, and know where to be strong and where to be flexible- demands that are of little consequence, demands that involve important issues or personal integrity, demands that affect major life directions, and/or demands that are dangerous or illegal.
Step Three Respond in a constructive way.
Non-defensive communication  :)o not defend or explain your decision or yourself in response to pressure. Use phrases like "I’m sorry you are so upset. I can understand how you might see it that way." Without fuel from you, the controller's attempts that worked so well in the past will fizzle. Choose time and place carefully. Lay down conditions for the meeting, announce a decision and stand by it – offer a suggestion that they not respond immediately. Anticipate their answers. Practice or role play. Consider how to respond to the person’s: Catastrophic predictions and threats, name-calling, labeling and negative judgments. The deadly whys and hows – demanding explanations and a rationale for your decision. For silent angry people, stay non-defensive.
Enlisting the controller as an ally When emotional control reaches an impasse, it’s often helpful to shift the conversation by involving the other person in your problem-solving process. Approach with curiosity and a willingness to learn.
Bartering When you want another person to change his or her behavior, and at the same time you acknowledge that you need to make changes of your own, barter may be in order. It’s win/win. It enables resentments to be put to one side.
Using Humor In a relationship that is basically good, humor can be an effective tool for pointing out to the other person how their behavior looks to you.
Step Four Be ready for some pushback or more aggressive responses. Often things will get worse before they then get better - our resolve will be tested - this is common in any type of relationship retraining. We need to have perseverance and confidence that both sides will eventually adjust, and it will end or reduce the feelings of being controlled.
Step Five Periodically evaluate the progress. Keeping a log of events, actions, and outcomes is helpful for this purpose. A lot can be learned from looking at the history - what works, what does not, and if progress is being made. All of this should be factored into our decisions of how we go forward.
I hope you'll find these resources helpful as you prepare yourself for dealing with your mother.