teenage mother
Refers specifically to a mother who is still in her teens, often with a nuance of youth and inexperience.
She became a teenage mother at 17.
young mother with gal style
Describes a young mother who maintains the flashy, trendy fashion and makeup associated with the 'gal' subculture, even after having a child.
That young gal-style mother always has flashy nails.
Compound of ギャル (gyaru, from English 'gal', referring to the Japanese fashion subculture) and ママ (mama, 'mother'). The term emerged in the 2000s to describe young mothers who retain gal fashion.