Honestly, I don't think A's motives made sense. There were 3 A's as far as I know: Mona, CeCe, and Alex.
Mona's motive was that Hanna was pulling away from Mona and spending more time with the liars. But Hanna only begun spending more times with the liars after Mona began sending the texts. And if Mona was only mad at Hanna for pulling away, wouldn't she be only texting Hanna?Perhaps it was bad writing, idk, but Mona's motives for being A literally make no sense.
CeCe's motive was that she was upset at the liars for wanting Ali dead. If that was so, why would she also torture Ali? Maybe its all part of the A game or something, who knows, but I think it is really poor writing on their part.
Alex's motive was that Spencer had everything and she had nothing. Then, why would she not just torture Spencer then? Why torture the other liars? Again, I think this is also really poor writing on their part.
Idk, I feel like if they were going to make the characters on PLL A, the writers should really give them better motivations.