The reason this feels impossible is not that you lack the words. It is that the words you have been handed are bad, and some part of you knows it. Almost every stock condolence phrase in English was built to make the speaker feel less helpless, and a grieving person can hear that in about half a second.
So start from the opposite intention. You are not there to fix anything, lift their mood, or find the sentence that makes it hurt less. There isn’t one. You are there to be a person who knows, and who is not going anywhere. That is a much lower bar than the one you have been setting for yourself, and it is the only one that matters.
Say the name. The dead have a way of disappearing from conversation almost immediately, because everyone is afraid that saying the name will remind the griever — as though they had briefly forgotten. They have not forgotten. Not for one minute. What they notice is that everyone else seems to have. Saying “Ellen” out loud is a small, enormous kindness.
Be specific. “She was a wonderful person” is true of everyone and lands on no one. “I still think about her showing up at the hospital at 2am with a bag of terrible vending machine coffee” is a gift, because it is proof that someone else is still holding a piece of this person. If you did not know them well, be specific about your own reaction instead: “I have been thinking about you all day.” Specific is what makes it real.
Say the awkward true thing. “I don’t know what to say” is not a failure. It is honest, and it is a relief to hear, because it means you are not about to produce a script. Most people would rather be sat with by someone visibly out of their depth than reassured by someone performing composure.
Do not hand them a task. “Let me know if you need anything” is the most common thing said to the grieving and one of the least useful, because it moves the work to the person with the least capacity to do it. They will not call you. Naming a specific thing, and then doing it, is worth more than any sentence: “I am bringing dinner Thursday, I will leave it on the porch, you don’t have to see me.”
Words you can borrow, verbatim, if you need them: “I heard about your dad. I’m so sorry. I don’t have anything useful to say, but I didn’t want to say nothing.” Or: “I can’t stop thinking about you. No need to reply to this.” That last line matters more than people realize. A message that does not require a response is a gift to someone whose inbox has become a second job.
And then the part almost everyone skips: come back. The casseroles stop after two weeks and the calls stop after a month, and the grief does not. A text in November about someone who died in August will mean more than anything you say this week.