Valmiki Ramayana Ayodhya Kanda Sarga 60 Shloka 16

वैदेह्याः Sita's, चन्द्रांशु सदृशी resembling the beams of the Moon, प्रभा lustre, अध्वना on the way, वातवेगेन or by the speed of the wind, सम्भ्रमेण or due to haste, आतपेन च or due to scorching heat also, न विगच्छति does not fade.

Just like the beams of the Moon, Sita's glow is not affected by the fatigue of the journey or by the speed of the wind or by the scorching heat.