Hae's errand that did not involve Adnan - Does it point to someone else?

The most interesting part of the podcasts and research to me relates to Hae rushing from school in order to take care of something before picking up her niece. This specifically points to a rendezvous with an outside person that clearly was not at the school. Someone else is very important to the story. The third crime scene appears to have to be connected to a person she knows that is outside of the school. I feel as if this is underdiscussed in the grand scheme of things.

What did she need to do in that small window? Was she contacted by someone to meet up? Is this person somehow connected to Jay or Don? Why would this meet-up cause Jay to point the finger at Adnan.

Where this trips me up is that somehow Jay becomes involved in the midst of the worst case of bad luck for Adnan. I have speculated that Hae may have been contacted by Don to meet on a break (http://viewfromll2.com/2015/03/19/serial-the-question-of-dons-alibi/), but then the rest of the day just would not make sense.

I tend to believe another person was involved that lured Hae from school and was connected with Jay. Jay is protecting himself and this third party with fear for his own life and the health of his loved ones.

Even if Don's alibi is not completely verified, the day's events might not make much sense if he committed the crime.

Who is this someone she needed to meet or errand she needed to run?

EDIT: Or is it someTHING, such as depositing the check in the ATM.

EDIT: I base this on

1. Her classmates and friends knowing she picks up her cousin/neice every day
2. She is running out of school at 2:20
3. What I have heard is that the cousin/neice's school gets out at 3:15
4. She tells Adnan and others she has an errand to run, which suggests something entirely different
5. No testimony has stated she refused to give a ride purely because of her cousin/neice
6. She appears to be running out of school when she has an hour to spare, less drive time