There are several reasons.
She's pretty good at Apex and seeing her make skillful/unexpected plays is entertaining. Apex is very big in Japan, as confirmed by playercounts, and that one cultural exchange thread >we had with 2chan yesterday.
Lastly, seeing Aqua (and really, any of the holos) genuinely enthusiastic about playing a game without being bogged down by the worries of life has its own relaxing quality. Plus Aqua 'tism is fun