While "current" can refer to a flow of something, it's a bit too literal and clinical for the emotional sentiment expressed in the sentence.
Here's why:
* "Current" implies a steady, predictable flow. The understanding between sisters is likely more nuanced and dynamic.
* "Current" lacks the warmth and affection that the sentence aims to convey.
Here are some better alternatives:
* "river": evokes a powerful and flowing image, with a touch of romanticism.
* "stream": suggests a gentle, continuous flow of understanding.
* "tide": hints at the ebb and flow of their relationship, with moments of deep connection.
* "wellspring": emphasizes the source and depth of their understanding.
The best alternative will depend on the specific tone and imagery you want to create.