This is the 11800th most frequent French word.
soutienne
There is no French word "soutienne." You may mean "soutien," which means "support" in English.
The word 'soutienne' is used in the subjunctive mood to express a necessity or subjective opinion about her supporting her friend.
Il est important qu'elle soutienne son amie dans cette situation difficile.
It is important that she supports her friend in this difficult situation.
Here, 'soutienne' is used in the subjunctive mood to emphasize a subjective implication of supporting a cause.
Que je soutienne cette cause montre mon engagement.
That I support this cause shows my commitment.
The use of 'soutienne' (first person plural subjunctive form here: 'soutenions') reflects a wish or desire expressed for the action of supporting efforts.