Sentient_Spacedust

Yeah, BB3s are unblockable, BB3s also have a skull on both the bottom left and right corner

BB1 - blockbuster moves that costs 3 or 4 move points, damage from them considered as "High".
BB2 - blockbuster moves that costs 5 or 6 move points, damage from them considered as "Very High".
BB3 - blockbuster moves that costs 7 or 8 move points, damage from them considered as "Ultra", plus, as stated above, they are unblockable and have unique blockbuster icon frame format (skulls added).

http://forum.skullgirlsmobile.com/threads/moisterrifics-complete-tier-list-1-5-0.921/

This is Moisterrific's unofficial tier list that includes all the characters and where they basically stand in power.

Diva is alright in my opinion, not my personal favorite though. Harlequin boasts the highest Fighter Score in the game and has good attack, health and abilities. Epic Sax is considered God Tier and is very good.

For me, Diva Intervention is really good, her SA can give you the possibility to get a large amount of hits on combos easy (even infinite combos) but if you don't like Eliza you won't find the utility. Harlequin and Epic Sax "always" be better on paper, but if you raise the meter gain (and have sekhmet's blockbusters) on Diva Intervention you can become unstoppable (like Eliza suppose to be jaja).

My personal recommendations include Blood Drive, Bad Ms Frosty, Bloody Valentine, and as a bonus for a bronze: In Denile.

Big Top Cerebella, Resonant Evil Big Band, Doublicious Double.
Pea Shooter Peacock optionally; she's a good support character which can give a huge boost to some other characters BB's like Big Band BB3 "Strike Up The Band", Parasoul BB3 "Inferno Brigade" etc.

https://twitter.com/sgmobile/status/977009559633121280

Neutral.

She changes elements all the time in an actual fight, but officially she is Neutral. If you're trying for the "Use a team of 3 different Elements" she counts as a unique element just like the other 5.

Nah... Don't worry. Just try to be more aggresive sometimes or you'll get bored.