Is it ok for me to say no to my mom when I'm the only one that can help her?

Hi there! Thank you so much for your question. I want to say that I really appreciate your insight into where some of this is coming from for you; you have an awareness that there is guilt (perhaps shame, too) and a sense of obligation. This is incredibly common if you grow up with emotionally dependent parents (we call it parent-child role reversal) and it is a cognitive-behavioral pattern that is so hard to shift.

My one sentence answer to your question is: Yes! It is absolutely okay for you to say no!
The trick to that though is follow through, and ongoing follow through not just for this one time.

You have children, so I think you can appreciate the concept of teaching independence and the importance of that. Imagine a toddler who has been carried everywhere they go for all their life, and suddenly you put them down and tell them they have to walk on their own. They are not going to like it, they'll show you all sorts of spicy emotions, and it will take lots of follow through with you not picking them up while they learn to walk. That is hard for both of you--them for feeling confused about the sudden change and for feeling like you no longer care, and you for feeling like you have abandoned them. You described this as having happened to a degree already.

Changing a pattern that you have had for most of your life means that suddenly your mother is going to be faced with a change in your behavior that is going to be uncomfortable and perhaps even frightening and threatening to her, and as a result she will eventually have to change her own behavior because she will not have you to depend on anymore. In the beginning she may absolutely feel abandoned--you have been her main support all this time. That can lead to all sorts of lashing out. Think of it like a tantrum. The reality of it though, and again seeing as you have children I think you can put this into perspective, is that you know in the long run this will pay off. She needs to learn independence, and you need your independence as well. 

I return to my statement that saying no once is not enough, and if you say no and back down it does more damage to the attempted change. Again... think of a child. If you are trying to teach a child to sleep in their own bed and not yours but you only make them do it for one night and then not after that... what does that say? Or worse, if you tell them they have to sleep on their own but don't stick to it when they try to crawl into bed with you later that night claiming they're scared... what does that say? Essentially they learn that, if they push the right buttons, they'll always get their way. Then you're left feeling exhausted and steam-rolled. However, if you consistently put them back into bed (if you consistently set boundaries with your mother's independence) they learn that you mean it, you cannot be manipulated, and they are left with no choice but to learn how to be on their own. Eventually they develop the tolerance and skills to do so. Independence for all!

This is easier said than done and it takes a high level of commitment in the beginning. Your sense of guilt will be your worst enemy at this point. You deserve the independence, though, and honestly so does she. I hope this is helpful and I wish you the best of luck!