My coworker hasn't rocked up to work today. She's never ever late, in fact, she's usually here an hour early. 

Whenever she has been off sick, my boss calls to tell me she's not coming in. When she has an appointment, she tells me or puts it in our shared calendar.

I really don't like her and, quite frankly, I don't want her to come in but I don't want to look like an asshole for not checking up on her if something is actually wrong. 

We're a tiny company (only 3 or 4 of us including her who work from the office) if that makes a difference. 