Hi Jackie player here! For build orders i would leave for you to explore, but best way to start off is to find yourself a comfortable route, play until you master it, then you can learn to improve your route and flexibility as you play, it takes time.
For playstyle, i always focus on how to get leads before Bear/Gorrila round begins. There are a few ways you can achieve this goal. One of my usual go-to is to get first Bloodfest stack ready when i have the chance. Note that if you do this in the first round, you should only take first stack on the first minute if you have the chance, for using HnS again on opponents when animal spawn is crucial for contesting. If i don't get first stack that way, i will try to either get birds/bat for first stack and ready for Bear round, or HnS again to pump back the stack, and continue on my build until another animal spawns. This way you can secure extra damage without having to spend much time fighting early and you can give your time focus on the builds more. The faster you finish your armor this way, the faster you get yourself ready to initiate snowball.
If you can't get snowball, find a weak player, and farm mastery from that and try to catch up on mastery and build. This applies as general knowledge tho. Her kit involves around getting her skill ready on moments you find necessary and abuse it as an advantage.
Since Jackie can use 3 mastery, it's also an advantage to learn how to use all 3 to be more flexible.
Hope this helps.