Hi BeBraveandBeKind
re your comment:
"To be fair, she is great in a crisis that requires practical help"
Did you actually ask for such help or did she shoehorn her way in without asking?.
By being or appearing to be as giving and helpful they can feel superior to others.
Narcissists sometimes help others and do favors because it gives them power over those whom they help. If someone helps you, you feel grateful and willing to help them in the future. This is normal and a good thing.
However, one thing you don't want in your life is to feel in debt or otherwise obligated to a narcissist because they will abuse this power dynamic, without exception. They will string you along either by using it as leverage or by demanding more than their initial favour was worth. They will remind you forever about how much they helped you when you were in need, and so on. This induces feelings of guilt in their target, in this case you.
Narcissists can sometimes be helpful and caring. However, more often than not, they only pretend to have these qualities. Moreover, even when they act giving and helping, they are not motivated by empathy because they severely lack it, and as a result, their help is often not very productive.
Narcissists are motivated by feeling superior and expanding their power, and so the only things that matter when helping others are receiving adulation, fame, influence, opportunities, notoriety, and other resources. They don't actually care about others because to them other people are just things to use.
Its probably also hard for you to set boundaries also because your mother here has really not encouraged you to have any.
Your selfish and self centered mother put her need for a love and or sex life ahead of you people as her now adult children and you've all suffered greatly as a result. Deal with any and all FOG (fear, obligation and guilt) here through therapy. Reading the Out of the FOG website may also be of some help to you.