For those either pretending not to get it, or who are so tone deaf and self centred they really don't get it, this is why a gift would be the wrong thing to do.
A charity donation shifts focus away from the child and the horrifying indescribable pain of their dying to some abstract greater good. Who fucking cares about charities when your kid is dying? Charity donations are typically given after death in memoriam.
Any gift forces the grieving mother to acknowledge or appreciate the gesture. this is emotional labour she does not need or want. Gifts are future and celebration coded, not "the worst possible thing that can happen to any parent is happening to you right now" coded.
Every "gift" that enters the house becomes an object that she will later have to decide to keep as a corpse-memento or dispose of. Parents in this position describe unsolicited gifts, even small or supposedly thoughtful ones, as minimising the utter horror of what is happening to their baby.
A gift prioritises the donor and their need to feel like a good person.
A gift prioritises the sender’s need to feel helpful and no gift can be truly no strings attached in this circumstance. The string is that the sender wants to feel they did something good or useful while the mother endures horrifying anguish.
Some people won't mind you sending a gift to try to make yourself feel useful and kind - and many will. You cannot know how it will be received and so it is far better to avoid altogether.
Sending an unwanted, un-needed gift is easy. Holding space for someone is hard, sitting in someone's pain, lifting the phone and talking to them, enduring their agony, listening to them, just being around them - this is hard.
Phone her, and if she does not want to talk to you that's fine. Keep in touch with cards, emails, with no expectation of any reply. At some point she may want to bring her grief to your door.
If you love her, your compassionate attention is the only real gift you can give her.
There are also many guidelines out there on how to support someone in grief, I suggest you read them.