OP, on reading your post, I got the impression that you actually do have a pretty good idea of what's acceptable behaviour towards you and not. You may not feel totally confident (yet) in following up on what you feel, but I would hazard a guess that you're spot on in your initial judgement of a situation. It just needs developing a little, so you don't then waver as you are now.
And please don't take it as a failing on your part that you're tempted to respond how she wants you to. She's probably very persuasive. And she's your mum, there's a lot of unnecessary authority that's been vested in her as a figure since childhood. And you're probably an empathetic person who craves a sincere and reciprocal relationship with her mum. At the same time, however, you've recognised the unlikeliness of this happening, which is helpful for you.
I really wouldn't berate yourself by saying you're 'terrible for trusting the wrong people'. I suspect that you've learnt a good deal from any contact you've had with her. Maybe you were indeed vulnerable to her in the past, but this probably isn't the case now. Use what you know now. It may not necessarily feel completely 'right' to you (again, yet), you might have niggling doubts - most decisions people make in life are accompanied by doubts. Decisions are not usually comfortable things to make. But here it's the difference between protecting yourself from discomfort caused by doubts, and greater discomfort caused by someone who doesn't take your best interests into account before following her own impulses.
Do be aware that the fact she may have made a sacrifice in apologising to you (loss of pride, whatever) doesn't mean you have to sacrifice anything in return. There is no point in either her or your aiming for things to become 'even' between you. You don't owe her anything in return for this apology, you really don't, you're not contracted by the rules of decency to compromise, give way or anything. She chose to make it and risk having it ignored. That's fine.
And in the end: what does this apology really change? Has she convinced you she will be treating you respectfully from now on? If this isn't the case, I can understand it's probably tempting to just accept it anyway just because a) she's being nice for once and that's unusual so you don't have a stock response for that yet and b) you'd feel guilty for not responding (because you are an empathetic person and automatically assume others are too), amongst other reasons. Again, it's normal to feel temptation. But I really believe you have more mental recourse to draw on than you seem to think, I pick up on it from your post & don't even know you - please have more confidence in yourself and stay strong.