Selina could have been baptized at an older age. Some families baptized all their children on the one day.
I would think that there were many reasons for doing this.
Sickness in the family, not living near a church, only one surviving spouse after the birth of a child and that could have made it difficult, many reasons.
My husband and his siblings were all baptised on the same day, he would have been 5 at the time. Come to think of it, I must ask his mother what the circumstances were in his case. They were on a farm some way from the closest town so that may have been it.