Time Smashers
Member
Back+2 is VERY dangerous to use when you're getting pressured with block strings, because it has a slow start up. I'd say 99% of the time, you're not gonna get it off before they start their next string, because most people that are pressuring with block strings are usually using the fastest string their character has.
After 20+ hours of playing jade in ranked matches, I'm pretty confident in saying you should only use back+2 to continue combos, punish long recovery moves (there are better options for this though), or if you think they're gonna jump at you and they're too close for up+3 (but not if they're crossing you up).
Ex Glow is her best option if it's a character with a really fast string. If you have no meter though, it really depends on the match-up (for example, down+3 pokes work wonders against Cage when he's pressuring).
In my opinion, B2 is jade's fastest attack that she has, besides the low poke. It has very low charge up time, contrary to what you said, and is probably the fastest option she has. Also, her overhead pole smash is probably better for hitting someone off a long block stun.