I feel like every day, my opinion on this case changes.
IF the red shirt turns out to be hers, I feel like she would have to have been wearing it when something happened to her. I just find that more believable than the perp knowing to grab it or finding it at the house and taking it. It is possible that even though she wears it to work, she also throws it on to just hang out at home or even slept in it since she would need to get up early the next morning. I know some people who sleep in their work/workout clothes so they can sleep in later the next morning and not get dressed. Now, we have no idea if it IS her shirt that was found, so this is all jmo and highly dependent.
I still have this feeling she left the house voluntarily. Between the dogs being in the basement and the claims of no sign of a struggle at the house/it not seeming like it was treated as the crime scene. What happened after that or why she left, I really have no idea. Could be she went somewhere with someone she thought she could trust/was well-known to her and then it turned bad. Honestly, before today I would have said almost 100% I believed it was someone she knew well; now today, I don't know that I'd rule out either a stranger or someone she knew of only peripherally but that had their sights set on her.
I just hope she is found.