Thanks Plunet...
I accept that travel requirements are changing constantly - indeed, I'm doing my PhD in the Netherlands right now and have travelled several times to the UK the past year (usually via Eurostar), so I'm quite aware of the need to stay on top of changes. But I guess the point is that A) there is no official section on Qatar's Ministry of Health website showing this information (only a news article at the bottom of their site, with Philippines not visible in the title on the Homepage); B) there is no information on Qatar Airways' own "Travel and Entry Requirements" information searcher, nor on the "Passenger Alerts" page; and C) Qatar Airways have a contractual agreement to provide travel that's paid for in the class of travel paid for (or to offer a refund of the difference if not possible).

Things are not easy right now for anyone, and I'm happy to give airlines etc extra flexibility if they need to rebook a flight etc (Qatar even cancelled a flight of ours last year, I understand). What's not acceptable is when they don't provide necessary/essential travel information even when you search for it, and then don't make any effort to make the resulting situation right for anyone (as I mentioned, about half the other passengers on the flight were also denied check-in).
Also I'll add, had we upgraded at time of rebooking to an "I" ticket (my recommendation, but she was thinking about if she could afford it or not) rather than the email upgrade to an "R" ticket, they would have rebooked her in business all the way for free. To say that an upgrade is not transferable when it's their own fault just doesn't cut it with me I'm afraid...

As a professional transport planner, I feel like I would be fired from a job if I were in charge of providing travel information to customers/the travelling public and failed so epically to do so...