Kaede's been part of the KSS act for several MM。tours (and H!P ones) so it makes sense that the others would know her, I think. Maimi said on H!S that even
she was super happy for Kaede and knows how much of a hard worker she is etc. I know Maimi's kind of a different case since she's the current H!P leader and all, but still. She wouldn't have maybe noticed Kaede as much if she hadn't kept being in the tours

. Also the musicals and stage plays probably have something to do with it.
Not counting KSS-only concerts, Kaede has performed as part of 23 different H!P concerts, musicals, events and stage plays. In her 4 years as a KSS, she's appeared at about
255 live H!P events in total.
1. ℃-ute 2013 spring: 21 cons
2. ℃-ute 2013 autumn: 20 cons
3. ℃-ute 2014 autumn: 11 cons
4. ℃-ute 2015 spring: 15 cons
5. ℃-ute 2015 autumn: 19 cons
6. ℃-ute 2016 autumn: 11 cons
7. H!P 15th anniversary live: 2 cons
8. H!P 2015 winter con: 2 cons
9. H!P 2015 summer cons: 20 cons
10. H!P countdown con 2015: 1 con
11. H!P 2016 winter con: 21 cons
12. H!P 2016 summer con: 20 cons
13. Hinafes 2016: 4 cons
14. MM。2013 autumn: 15 cons
15. MM。’14 spring: 6 cons
16. MM。'16 spring: 6 cons
17. Bokura Karin na Shounen Gasshoudan play: 19 perfs
18. LILIUMU musical: 19 perfs
19. Neganega Posiposi musical: 8 cons
20. J=J LIVE MISSION 220~Code3 Special→Growing Up!~: 7 cons
21. H!P New Fes! II: 4 cons
22. H!P ANNEX Kobushi×Tsubaki: 2 cons
23. ℃-Fes! Part 2: 2 cons
So... yeah. It's no wonder
everyone knows who she is, lol.
(Source is her Wikipedia page, total number could be off by a few because I can't math but it's somewhere around 250.)
EDIT: Lol, 12th gen only hit their 100th MM。concert performance earlier this year. Which means I think Kaede may have performed more times than 12th gen if one includes all the KSS cons/events.