In old times it used to be a bad thing to be over a certain age and single. The same used to be true in Brazil, and this expression designated these women over 20 or 30 as "titias" (aunts).
Nowadays it's still used to tease someone, specially older sisters that are single but with younger sister/brothers (or even most of her friends) that have already married.
The direct translation would be "stay for aunt" or "become an aunt". That doesn't make much sense in Portuguese if not used as an expression.
- Desse jeito vai ficar pra titia hein?
- Se sua irmã não arrumar um namorado logo ela vai ficar pra titia.