When a girl from tinder says she's not over her ex and isn't ready for a relationship after a date, is it BS?

The truth is that it doesn't really matter what her motivation was. There could be a million different reasons why she decided to tell you what she did. If you worry about it you will drive yourself crazy. It isn't worth obsessing over because you don't know where she is coming from. Let it go and move on, not only will you be happier but it will also convey your confidence and self-acceptance to others. It's a good opportunity to practice reminding yourself to accept who you are and accept her for who she is, unconditionally. Don't worry about what others think and do so much, you can't control others and it will only make you unhappy to try. You can only control yourself, your thoughts and actions. If you think it's because of something you said or did then you can work on that and move on. What's important now is that you leave her the space she needs and keep improving yourself. "We can't make others love us, we can only make ourselves worthy of loving"

If you don't like her behavior and feel like she's full of baloney then move on.

she's not into you. not the end of the world. move on to the next one

She thinks she is being kind and she is not interested in you romantically

She was letting you down as easy as possible.