Could a man with an o blood type be the father of a child with type ab blood?

Normally, that would be impossible. AB types usually have 1 A allele (gene-version) and 1 B allele, 1 from each parent. O types normally have no A or B alleles (as these are dominant to O alleles, so a person with 1 A and 1 O allele is simply A type).  

There is rare exception (much rarer than eg adoption or infidelity) known as the cis-AB gene, which can pass on AB blood type with a single allele. But that is a whole  other story.

you can show her once, and if she doesn't do it, do what i do: i take away one of her privileges until she learns. it worked for my sister but note every child is different. or you canput her on 'time out' if she doesn't learn.