Also, the dogs were still locked in the basement leans more toward Mollie either had not returned or had just returned.
But without knowing more about Mollie's usual routine/behavior with the dogs, hard to know how quickly she'd let them up from the basement on returning.
I know if I locked my dog in the basement and I wasn't down there too, he'd whine and complain til I either went down there to be with him or let him out.
Possible, esp since these weren't her dogs (?), that Mollie didn't have a close relationship with the dogs. And that she returned from her run, sat down in her jogging clothes to do homework and left them down there still. OR, that she came back from run, let them out and then, as someone suggested last thread, put the dogs in the basement when a visitor arrived.
But, yeah, with the limited information we have, seems Mollie was either on her run or returning from her run when the events transpired.