There are two main Jaina builds I use:
First is a standard burst build that basically insta kills anything that thinks they can play the game.
Second is for keeping alive against dive heroes (i.e Zeratul, Butcher, Tyrael, and Illidan).

No matter which one you are using play smart, and position well. You are still a woman in a dress, hate to break it to you, but that isn't armor.....

Focus on wave clearing, and during objectivs you can easily catch someone out. The increased slow on your passive makes it insanely easy to get picks in a fight, whoever is caught out won't be escaping quickly. Same goes for you though, if you can find a magical dash for Jaina feel free to be frontline, until then sit back and throw snow like the good girl you are.

I will lump these two together mainly because, your playstyle stays the same after 10. You have the water elemental and you still throw snowballs, so keep it up.

For the second build you may ask why I take wintermute instead of bolt. While bolt is still amazing and if needed I recommend you take it, but as for me I have 2 reasons why I don't usually.
First: I have 2 defensive mechanics already, and I play ranged enough to know my positioning quite well.
Second: With wintermute your elemental mimics your skills, that also means cone of cold roots(even from when your elemental casts it). The best defense at times is a strong offense, and let me tell you Jaina is as offensive as they come.

Use the wintermute range to initiate a fight, and immediately cast cone of cold from your elemental to root that person in place. Your team collapses as you throw extended range blizzards on that player, and the fight has begun with one person hopefully being dead.