Type A mother, Type O baby:

(1) As before, Type A Mother must be AA or AO: an AA mother cannot have a type O child:
 

Mother
Father
Children
AA
AO or AA
A only
AA
BO or BB
A or AB
AA
AB
A or AB
AA
OO
A only

(2) So, if Mother is AO
 

Mother
Father
Children
AO
AA
A only
AO
AO
3/4 A, 1/4 O
AO
BB
1/2 B, 1/2 AB 
AO
BO
1/4 A, 1/4 B, 1/4 AB, 1/4 O
AO
OO
1/2 A, 1/2 O

AO mother includes all putative fathers, if & only if they carry at least one O allele.