It's not as easy as saying you won't be upset, you have to take action, just putting out a mouth beep isn't much help.
Your mom must be in a lot of pain and upset when she loses her support. At this time, you have to accompany her more, give her more care and warmth, let her feel that she is not alone, she still has someone to rely on. Yes, you have to grow up to be her strongest support. At this time, she is very fragile, and may even have thoughts of suicide, you have to watch over her. One of my classmates' mom jumped off a building after her dad passed away in a car accident. That's why companionship is the most indispensable thing in such moments. Only if she doesn't think she's been left behind and only has herself left will she have a little more hope for her future life.
In addition, you can't say that she shouldn't be sad, where is it possible not to be sad about something like this. You have to let her cry out if she wants to cry, tell you if she has pain, tell you, you are able to understand her, your shoulder for her to lean on. You have to talk to her more, let her speak out her inner words and vent her inner emotions. But you don't want her to be immersed in pain and crying. When this is over, you can take her out of the house to do something she's interested in (such as square dancing, yoga classes, etc.), so that she won't be bound by the past and won't just think about the past.
Only if you become her dependant and take her to create a better future can she really come out of the pain of losing her dependence. And only by doing so will her life get better and better, instead of being shrouded in shadows all the time. In fact, there are times when an outsider coming in and pulling the plug is really especially helpful, so your help is something your mom needs very much.