I found it a bit odd as well. I actually find Cruella's obsession very bizarre. And also, how Chloe hates her right away. It's not like if she were a murderer… her crime was stealing pussies, it shouldn't be THAT hard to change and redeem yourself.
"You're a disease, and I'm the cure!" - Marion "Cobra" Cobretti

She bought Dipstick from Roger and Anita and they told her about the incident with Cruella plain and simple.

its possible she read about it in the papers and when she got dipstick it probably came up. Although how she was able to purchase dipstick in the first place is beyond me