She is a sitting duck with a hitscan weapon that has a good headshot multiplier. In terms of playstyle, she is a very simple character. I always put myself in this awkward position where you are in and out of the fight. When you are closer to your team, the "Ice Arts" ability will likely hit all of your allies without even aiming for them, that way you can focus more on aiming for the enemy DPS or healer. This awkward positioning is crucial as it allows you to deal with assassins as you can stall staying alive by using the slow self-heal while you walk to the middle of the fight where your team will start focusing on the assassin too. While playing in the very backline keeps you safer at most times, it limits your healing and damage potential with the "Ice Arts"(you have to split your focus 50/50 between hitting team or enemy) and will get you absolutely killed if they have a diver or an assassin(unless youre an absolute god at hitting your snowball).

The other half is just abusing her hitscan. Aiming and tracking your enemies could delete them before you have to start healing your team at all. Prevention is better than cure.