Hindsight is 20/20. The idea of looking back for red flags, I think that sets you up for trying to take the blame for her behavior, that you "should have" known it was going to happen like this. That thinking is every kind of wrong, because with the next relationship, you're going to be looking out for this type of normal behavior and think it's going to end the same way, which is probably not true.

People don't trust from day one. If you find someone like that, run in the other direction, because that's unsafe. People slowly learn to trust more and more. That's not a red flag.

People also run hot and cold. If someone backs off a little, they could be busy, they could be scared because the relationship is getting deeper (which is actually a good thing, it's a test to see how you're going to handle their emotions) there are a million reasons why someone might take a temporary dip. It's classic for avoidant people that as soon as they see someone pull back they cut the relationship off - that behavior is due to a mental disorder, don't start thinking like that.

Red flags you said you now see at the beginning of the relationship - take another look at those, because it could be very normal, someone who just isn't quite 100% on board yet. In the beginning, that's normal, you just want to see some movement, that they are dropping their self defensive behaviors and are trusting you more.

I'm getting repetitive. In a nutshell, I think you're trying to blame yourself for not being a future teller, and the red flags you're looking for in order to find a way to control an uncontrollable situation aren't red flags but are actually normal behaviors.

Here is a list of actual red flags.
15 Red Flags Not to Ignore In Any Relationship
I don't think they apply in your relationship. I just think it was bad luck.