According to wikipedia article of Vritra -
In one verse of a Rig-Vedic hymn eulogising Sarasvati, she is portrayed as the one who slayed Vritra. Mention of this occurs nowhere else.
The verse the article mentioning is 6.61
I think it's not vritra but son of Vritra, Vetra with similar name as this story is found in Varaha Purana and Mahabharata too
As per wiki article of Gayatri
She further developed into a fierce goddess who could even slay a demon. According to Varaha Purana and Mahabharata, Goddess Gayatri slayed the demon Vetrasura, the son of Vritra and river Vetravati, on a Navami day.
Does Rigveda call the demon vritra or vetra?