Sydney had reached a new low and it was way too low for her. Why would she have given the poison to anyone? Why did she give the poison to Leander?

What did Leander do to her when she came back to him?! 

Leander didn't tell me everything that happened when she came back in his life but I think Leander didn't treat her right. At this point I wasn't even jealousy that Leander allowed Sydney in his life even after her killing our pup. I was worried about him.

"But I overheard you speaking to this ...