Thanks for the replies. I did check the handbook and it states that 5 unexcused tardies will be considered 1/2 day unexcused absense. This week's AU1 was changed to TU0 which means she made it before 8:30 apparently. Dad is still going to have a talk with mom and we actually discussed him offering to pick up DD before school, etc.
I can understand where those of you think that being late is not that big of a deal. She isn't absent because IMO mom doesn't want her during the day (mom sleeps a lot according to his DD and from DH's own experience while married for 13 years). DH does think it's a big deal and is only a small part of the BIG picture of this mom not putting DD first in anything.
We already got DD an alarm clock which she doesn't hear sometimes (same at our house

) and we talked to her about getting up and getting dressed on her own, land wake her mom up to say that she needs to go to school. And we also talked about DD keeping an eye on the clock so she knows when it's time to leave (8 is late!) The kids are supposed to arrive at school between 7:45 and 8:10. The 1st tardy is 8:15 and 2nd is 8:20. His DD's class does Rocket Math and she would have more time to spend practicing if she got there earlier. When she's late, she doesn't get to do the practice test before she has to do the timed test. Small thing? Probably, but still so frustrating for dad.
I'll let ya'll know how the talk works out. My advice to dad was to keep it non-confrontational (even if she gets ballistic) and to ask how
he can help her get their DD to school on time all the time.