She should have put the letter in an envelope first, and then put the address and stamp on that.
You're obviously not old enough to remember aerogrammes, where the letter was the envelope.
Why not a seoladh??
a seoladh - "her address"
a sheoladh - "his address"
I thought bit was ‘a seoladh’ when it referring to a female?
"his address" isn't referring to a female.
Also she forgot to write her own address on the back.