It is unreasonable to expect other people to manage your anxiety levels once you are an adult.
I frequently have to do this and it is frustrating, exhausting and sometimes causes me quite a lot of anger and resentment. And I am a patient person.
My tactic is to say: ‘I don’t know’ when asked about all sorts, including the likelihood of terror attacks, because I don’t and also because discussing it feeds her anxieties.
Sometimes when she asks me my opinion on something I do know about, I still say I don’t know because I know she won’t like the answer and will blame me for upsetting her even though she asked a direct question.
Why should I have to second-guess like this? I am not her mother. I am not even older than her.
Her family, who indulge her and therefore feed her anxiety, will also sometimes blame me or others who've told her an inconvenient trut because they will have to spin elaborate lies to show why what I’ve said will probably happen, won’t happen at all.
I’ve even experienced her family insulting me in an effort to placate her, as in: ‘Limited doesn’t know what she’s talking about’ (when I do and I’m sitting there) or her saying: ‘Limited. My husband says you talk shit’ while he’s sitting there and grinning at me behind her back as if to say: ‘I’m sorry. Please take no notice. You know what she's like.’
Lying and pretending everything’s fine is no good either because she’ll say: ‘But do you really think it’s not going to happen?’ Sometimes she will accuse people of insulting her intelligence. 
She can sometimes get aggressive and insulting if the pretend answers aren't good enough.
That’s why I go for ‘I don’t know.’ Her family haven’t learned that yet. They might do, but I don’t hold out a lot of hope.
She asks for opinions, but just wants to be reassured. I realise some people on this thread might not ask, but I still think it’s unrealistic of them to expect people to stop saying unpalatable things
I am able to brush it off eventually with wry amusement, because luckily for me I don’t have to live with it constantly. If I did, it would drive me nuts.