So basically, I feel like I need to firstly analyse how 'woke' the bisexual person to see if he/she's a decent bisexual person. And I didn't come out to her because I've already seen typical red flags from her such as "Oh, I don't need to label myself, everyone's on a spectrum". When I asked her, for example, what kind of guys and girls does she like, she said she "didn't know, all she knows is that she's attracted to some women". Basically she always gave very vague, non concrete answers.

This actually sounds a lot like me. I think people are too invested in sexuality labels. In my ideal world, you wouldn't try to figure out if someone is gay/straight/bi before asking them out, you'd just ask them out (and immediately respect a "No, thanks"). I also don't know how to summarily explain what I'm attracted to, because everything I can mention comes with a dozen exceptions, and exceptions to those exceptions. It's a matter of "I know hot when I see it." I'd also give vague, non-committal answers if someone I didn't trust very well was asking.

Why don't you feel safe around this person? You say she's your friend. Have you ever talked politics with her? Gave your own opinion on current events? Maybe the best way to get the answers you want is to be more direct. Not necessarily point-blank doing a survey of her attitudes, but bring the topic around to these issues and see what her opinions are.