she usually is testing the water, she sees you as a potential love interest but also is deciding so just play it cool and be yourself, if it doesn't work out romantically then at least you'll have a cool new friend
It sounds like after the two dates where you constantly had something to do, she now wants to get to know you and see if you are happy in each others company without having an activity to talk about
If on the first two dates you paid she is probably just trying to be nice and take a turn to treat. She enjoys your company and would like to casually have lunch with you.
If on the past dates you have both paid your own way I think her inviting you to lunch is saying she enjoys your company but would appreciate it if you took turns treating so that it feels more like a proper date than just friends. Just my 2 cents.
She wants to talk to you to politely end the relationship, if you can call it that. Or that she is interested and finds it a more relaxed way to have a conversation. You will only find out if you accept the invitation.
Thank you all for your opinions really interesting takes on the situation. I think I will just keep meeting up with her until she wants to be in a relationship with me, as she already knows I like her but said it was too soon to make it official.