She can probably transfer it with approval from both schools.. cancel the visa and immediately apply for an extension based on working for the new employer.
Still a good 2 months away just wait till July and see.
At this point I don’t think anyone knows, and they allow for end July to hope that things are back to a “new normal” as the government has been always talking about.
Do in country extension if you can meet the requirements, otherwise go to Laos before July 31 . Laos is already easing restrictions so it may be an option soon.
After you leave the company and cancel the work permit, you’ll be permitted to stay until the end of July under the current visa amnesty which gives you time to leave, or sort out your next visa.
Schools should open up by beginning July (if not sooner) so you can start to make arrangements then.
Your extension of stay will be made invalid as soon as you leave. You have to cancel that and then under normal circumstances you would apply for a covid19 extension with embassy letter (Immigration still accepting them if you can get it).
If the law passes (which it has not today yet), then you shouldn’t have to do anything (maybe cancel).