Edna’s knowledge of the track is legitimate.
The passage describes Edna as being incredibly knowledgeable of the track. It says, "there was certainly none who knew it better." This quote shows that the speaker regards her as an expert in the race horse. Even though it says that "she sat between her two companions as one having authority to speak", we don't actually know how her peers view her knowledge. We also don't know Edna's feelings about her friends, and since there is no real dialogue from Edna we do not know if she is being boastful.
