I see the thing is when shes chasing you is that sometimes shes can be closer than you think so maybe the reason she got you in the stall was because she was right behind you.
I do see what your talking about with her field of view but personally I never encountered any issues with it normally I run into a room and crouch behind the open door and she loses me so that's something you can try
She is supposed to be slower than you when she eats 2 students maybe shes not I always assumed she was due to the fact I was always able to escape her when she had 2 prey.
I will say this some of your criticisms could apply a bit more to another Pred Satie shes the third one you unlock and shes basically Bella on steroids Bella the only Pred affected by the apple trick so Satie will just eat you anyway and shes faster than Bella the only 2 downsides she has is shes has louder footsteps than Bella and can only hold 2 prey instead of 3 I like to think she could hold more but according to her lore she wants to keep her figure so I like to think she holds back her true power shes still very scary but personally I still had fun with her despite this because I just had to be more careful and if your wondering no apples aren't useless now they can still be used to fill saties belly to make escape slightly easier.
as for the other 2 preds there not exactly Bella clones they have things that make them different The fairy is a completely silent Pred with her only sound cue being the gasp when she sees you but she can only hold one prey so feed her a prey and she will leave you alone for awhile. and the lamia is also a silent Pred she does make the sss sound snakes make though but its hard to tell where she is just by that one sound shes large and slow but still can move slightly faster than you to catch you she is the hardest to escape I only escaped her once and she can hold at least 5 students at a time maybe more I don't know the exact number and she gets the other students to snitch on your location I haven't beaten her yet but shes a fun challenge.
Bella I would say shes the second easiest to escape her belly the fairy the easiest though that doesn't mean its easy Satie either has the same or better belly strength than Bella and the lamia has the strongest even with 5 students she digested us all her stomach strength is insane and I love it.
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I think part of my problem is I was trying to Metal Gear it, but the small map has little to no hiding spots that actually work and as for the bathroom thing I was far away when I hid, and she got to me after 20 seconds. It was most likely caused by me overusing my laptop or a bug that rarely happens. My mind is clearer now that I am not drunk and got some sleep, so I realize how stupid I sounded. I do think an easy mode for those who are having a lot of trouble like me would be a nice addition or at least lowering how far the preds can see since they can spot you from one side of the map to the other which does make stealth less viable and make the pillars a bit bigger so they can actually hide the player. Maybe Ghost will read this and consider these.
(Edit) She's about the same speed as the player but has better turning and can B-line towards you when she's eaten another student. I think she's supposed to get slower per prey, but it's not working as intended.
Personality I don't try to stealth it I feel like the game is more about getting as much done as possible while taking the measure's to secure yourself like if I can confirm Bella is on the top floor or is at least heading there I will take the opportunity to run to cover more ground and get more done quickly while also being careful around corners I usually follow other students around corners if possible to avoid surprises that's just how I play you can hide from Bella though I would agree that the map doesn't have enough hiding spots but you do at least have enough for her to lose sight of you if you know what to do at least in my experience