Your eligible contribution is figured this way
Jan $6900 + $1000 catch-up
Feb $6900 + $1000
March ditto
April ditto
May $3450 + $1000
June
.
.
.
December $3540 + $1000
Total $67200 divided by 12 = $5600.
Since an HSA account is in one person's name only, you can't take advantage of her catch-up provision. But she could contribute $1000 X 4 / 12 = $333 into a separate HSA account in her name.
