Hmm - reading your ideas...
My only one myself - and feel free to reject this and spit on it...
I'd introduce the LGBT community centre as a mixed bag. But they're mostly good. Angelic.
And the protagonist, we meet trying to figure out a way to get her sister back. And she's desperate and dirty and flawed. (Admittedly, my big worry with this is if anyone would follow a character who is desperately trying to bomb a LGBT centre which is why you'd probably have to explain straight away and make sure there's a huge dose of empathy.)
Hmm - you could even start it off with her moments away from planting a bomb and we go back in time to explain why...
Anyways, by the midpoint, we learn why protagonist desperately wants to get sister back, and we learn she was also there (I can't help but feel this discovery should come later on). It feels like a twist.
By MP, we should learn there's some bad apples in the LBGT cult. Like DPG said in his post. Make sure they can put up an argument for why they're doing what they're doing.
You'd have some real conflict - if they actually had solid reasons for keeping the sister there.
Perhaps the older sister has history of violence? Or escaped a mental institute or something. (These are pretty awful ideas, but, whatever gets the ball rolling.)
I'm gonna quote Aaron Sorkin about that conflict thing...
"Conflict isn't just knuckle-boxing. Conflict can be a war of IDEAS. And you want the competing ideas to be equally strong."
I got that quote from here...
https://www.reddit.com/r/Screenwriting/comments/4zpcz2/i_took_aaron_sorkins_masterclass_heres_my_cliffs/