The 2 entry limit is by LAND. By air there is no such limit although questions will be asked if continuous entries are made with little time out of the country. I think she is out of time to get a visa from Phnom Phen, No appointment is needed but it takes 3 full working days according to their website and the soonest she could apply is Wednesday 16th, therefore collect on Monday 22nd.
She could go to immigration on 17th and apply for a 30 day extension, I think they will overlook the overstay as they were closed. She should have gone yesterday of course but that's history.