Valid question. She said she'll be taking interviews with media so I imagine they'll ask that.
My guess at answers:
1) She had moved cross continents less than a year prior. Shipped belongings, bought a car, etc. That's expensive and exhausting - Canadian contracts are usually a lot less lucrative than US ones too. If I were in her shoes I'd do my best to try find a solution without leaving before making yet another move (3 in in 4 years).
2) I'm guessing she believed Shelby in June but doubts grew after the full judgement was published in the off season.
3) something changed within the team, likely to do with Shelby being coached by Jerry. If Schumacher didn't tell GDS til mid June about the ban, did he and Shalane tell her ahead of time about the (probable) coaching situation? Did they tell Lucia Stafford? What do you do if you're Lucia Stafford and you sign a Nike contract, rent/buy a place in Portland only to find something out you don't like? What if they started out following the rules of the ban but started to break them?
4) so you want to leave, who is going to coach you? Where do you go? That takes time to set up.
From a combination of the above I could see it taking until now to make/announce this decision.