The reason that Shirley's testimony was invalid because she's a minor and by that, that memories about the robbery that she remembers could harm her and would most likely be susceptible to the suggestion. That is why the court would make her testimony as invalid and wouldn't consider it in any way even though she is the witness of the robbery.
Squanto became a guide to the Pilgrims, helping them to survive in their new home. By the fall of 1621, the members of Plymouth colony had gained a lot of knowledge about farming,fishing and hunting from Squanto