Could she tell i was checking her out?

i was walking through the park and i saw this gorgeous girl coming in my direction and when we passed we sort of stared at each other, but when she passed, i wasnt done, i turned around to see what else she had and i saw her staring back, she didnt looked creeped out but wasnt that funny giggling either just a casual expression, and i quickly turned back and moved on, im 15, shes probably the same if that matters it was pretty embarassing but how did this girl know...