Alina can learn anything she sets herself to learn.
The main issue with 3As and 4s was only one: risk, reward.
Harder tech elements mean more risk of problems with executing said hard tech elements.
You can see that even in a "regular 3" program, Alina has the hardest one (hardest program without a 4 or 3A of the current seniors, she also had the hardest one last season). Now she does a FS with two different 3Lz combos, it has inherent risks and executing it to perfect (as she did a bunch of times this season) requires a lot of skill. I would argue that as much skill as it takes to execute a 3A program or a 4 program.
It is a different, but equivalent, high level of skill, if it wasn't lots of other skaters who have the six 3s would go for it.
Alina was developed as a Junior for her first senior season using the best rationale of risk x reward available then, having her do 4s that could misfire was not a smart more then (same with a 3A), so she was not pushed into them. She had stamina, solid 3-3s, they used those instead of adding a "less solid 3A or a less solid 4s". She obviously did try them, 4s for sure, in training, everyone else did. Tara Lipinski in that documentary episode about Surya Bonali stated that she practiced 4s, I'm sure lots of other skaters did and do practice 3As and 4s with varying degrees of success rate.
To make a jump really worth your while to use in competition you have to land it in practice say 70% of the time, if you have "nothing to loose", you can throw stuff out there and see if it sticks. Alina was never a "nothing to loose" skater, when things in her Junior Season clicked into place it became clear she would move up and with Olympic team chances, then she had to get her success rate up to those 70% or better (it was, say, in the high 90% there, as mentioned by Daniil after Worlds). Figure Skating requires that you have the tech, have the nerves and have the health all at the same time. And you only get one shot at each program per competition. So, it is that moment, what you do then and there is what you end up with as a score.
For this season, adding a 4s for Alina and working actively towards that didn't make as much sense developmentally wise. She had the best 3A and 4 less tech, she had room to improve on other things that could add GOE. Her team worked with that. It looked, from the new judging recommendations, that the risk reward wasn't quite there yet.
Then it got a bit more there, via a skater with a 3A that while not at a 90% success rate could also be done in combo and could be executed when landed with a pretty rewarding GOE. Hard tech also carries your PCS to higher ground over time provided you have other elements to back it up. This season we have this case.
Alina's team probably looked at the reality of how the season was playing out and made a few decisions, for this season it was to stick to the original plan, work for those GOE bullets, she has been hard at work for that. This work will pay out in the long run, whatever the strategy. For next season, they are probably going to up her tech, with a jump that is most comfortable to her of the new arsenal of 3As and 4s. My bet is on a 4, because I don't think that adding both a 3A and a 4 at the same time would be smart right off the bat unless she gets both to 70% during training which is a tall order. 3As and 4s are added to competition programs lots of times with 50 or 60% success rate, because building them up to 70% or more, requires competition experience with them to bring solidity.
So far she seems to be following her team's "4 acquisition" blue print, in interview with other team skaters with this jump they describe going through a similar process than the one we can observe with her, near the end of a season they start training the jump with harness, then after if becomes good, they try it without harness, after they land it a bunch of times without harness they move it into their program layouts.
We will have to wait a bit to see how it goes for Alina, but she is training them (not right now in the lead up to Worlds, but trained them this season after GPFinal), since she is a gifted technical athlete, a great hard worker, I'm sure some positive developments will come from her training.
For this year's Worlds, her mission, and she chose to accept it, is to have clean skates, show her amazing skills, hit GOE bullets for her jumps and amaze us all.