As MM has no problem with private massive events once she is interested in the topic and she can jet around the world to attend them I would say that shyness is not her (main) problem, but work shyness. She seems to be nice enough privately but sadly she seems to be self-centered as well (she lets her 80+ year old in-laws down as well as her husband).
She is very lucky that ML is her sister-in-law and not someone ambitious like Sofia in Sweden, because then the contrast would be very visibile. At the moment Harald and Sonia are doing a fantastic job with good approval rates, her problems will start when she is acutally Queen and part of running the show.
In today's society less and less people will be happy with the concept that the highest position in a country is determined by birth rather than open to everyone. As a monarch you can prevent these line of thoughts a bit when you are doing a great job and you are likeable. But that involves work. Turning up in little house in the parie wardrobe twice a year will not be sufficient to keep the Norwegians happy and she might be ill, but is never ill enough to do fun events she is interested in, so that excuse is lame, too.
I have a chronic illness and haven't unfortunately been able to work for 11 years now. When I have the energy and I'm feeling well, I do all kinds of fun stuff. In between those moments I'm at home feeling unwell but no one rarely sees that.
So for the outside world it might seem that I'm lazy, just slouching at home watching movies and then (occasionally) taking short trips somewhere or going shopping, going for a coffee etc.
Just because I don't work and probably never will be able to do that anymore, I hope no one wants to take my fun days away from me. The mental energy I get from them, is the strenght that carries me over the bad periods, even though the fun days often drain me too.
I know MM wasn't working to her full potential even before she got ill but the situation is different now. I don't think she should have to give up everything, just because she can't work like she "should".