I believe the place where her car was found is significant. Tualatin Hills has some of the most popular baseball fields in the area, and she would have spent a lot of time there watching her kids play. I don't think it is mere coincidence that her car ended up being left behind there.
One thing that remains unclear right now is the length of time that her car was parked at Tualatin Hills. She disappeared sometime on Monday, and the media alerts started going out late Tuesday or early Wednesday. Her car was not found until late Thursday afternoon. Now it is probable that the car had been there all along since Monday, and people didn't think much of it until word got around that she was missing. However, it is possible that whatever happened to her happened somewhere else, and those responsible didn't drop the car at Tualatin Hills until sometime between Monday and Thursday. But given that the police have stated that they do not think foul play is involved, I tend to find this scenario unlikely.
So I would agree that the most plausible scenario is that she left of her own accord. If one were to hatch a plan to get away, it makes a lot of sense to start from someplace familiar. The spot where her car was found is perhaps 50 yards away from the #67 bus line. From there, one can take the bus to the MAX light rail station at 158th and Merlo. At that point, the possibilities are almost endless, and one can disappear into the wind. The MAX goes to downtown Portland and eventually all the way out to PDX Airport.
If she did leave of her own accord, what is unclear is what her motives and endgame were. She does not strike me as the type who would just abandon her life and loved ones and run off with some new distant lover. So what do we know? Her son said on TV that she had been despondent in the days leading up to her disappearance. We also know that some of the stickers had been removed from the back of her car when it was found. Taken together, those clues suggest that possibly some latent resentment toward her kids was unleashed by whatever the final triggering event happened to be. If she decided to go somewhere and end her own life, she apparently did not leave a note behind. But perhaps the car, left where it was, with the stickers partially removed, was intended to serve as her final statement, and she did not want to be found after she did what she was planning to do next. It strikes me as a particularly cruel thing to do to one's loved ones, but people who find themselves in this state are usually not thinking rationally. It is not a good sign that there have been no phone pings nor activity in any of her accounts since her disappearance.
This whole story is just incredibly sad, and my heart breaks for her friends and family. They deserve way better than this, especially her kids. The uncertainty and anguish involved in not knowing where she is must be devastating. I pray that either she is found safe, or that her loved ones receive some closure in eventually knowing what happened to her.