experienced mother; senior mom
Refers to a mother who has more experience in parenting, often used in contexts like school or neighborhood communities where she can give advice to newer mothers.
I got tips on child-rearing from an experienced mother.
I look forward to talking with the more experienced moms at kindergarten.
Compound of 先輩 (senior) and ママ (mom), a straightforward modern coinage reflecting the common use of 先輩 in social hierarchies.