1. Yes, it's valid (like Tsimanouskaya - we have this kind of experiance).
2. She can start with our nationality abroad since 20 june (but she must be approved as you said but via WA meeting
Then her mandatory waiting period to represent her new country ends
https://pzla.pl/aktualnosci/13751-maria-odzik-z-polskim-obywatelstwem
The next step will be the decision of the special World Athletics panel responsible for changing the national colors. We don't know when he'll get back together. Of course, we will lobby on this matter and we will do everything to ensure that Maria can start in the Polish Championships at the end of June. If this is handled smoothly, we will see her at the Olympics in Paris. She already has the minimum - explains Tomasz Majewski, vice-president of the Polish Athletics Association and head of the Olympic mission.