I also have wondered why people might not be direct but these days I try not to think about it too much, there’s usually not much we can do about it as it’s their pattern.

It sounds like you approached her about responding in a timely manner about movies and she did respond positively, but still delays about other activities?

Have you tried after a reasonable length of time (a few days say) of no response just asking someone else or making other plans? It sounds like you’ve given her lots of opportunities so it seems fair enough for you to get on and make other plans in absence of a response.