My 5 yr old niece

Patient: Hi, My Niece who is 5 years old told me as we stood outside her school that she saw double.. what happened was that her two friends were standing in front of a fence that had snow behind it, they were chatting about lipgloss and my niece told me she was trying to grab the other fence, cause she had seen two… she was staring intently at the lipgloss in her friends hand.. she was fine for rest of day then 4 days later, today, she said as she was speaking to me while focused at the wall behind me that she saw double/blurry.. everything else is fine… how concerned should i be!

Symptoms: blurriness/double vision at moment of staring, lasts 1 second or 2