Why does she do it? Because it's fun! And girls just wanna have fun.
The trick is to convince her that just a much fun can be had in other, more acceptable, ways.
In addition to (or rather, in conjunction with) the excellent suggestions from other posters, have you tried playing 'swapsies'?
This is a training game to redirect a dog's focus away from contraband and onto an object that is acceptable to chew, and ultimately to teach them to choose wisely.
Whenever you find your pup chewing her bed, you give an interrupt signal*, and when she looks to you then give her something else, something she sees as a higher value. You are swapping the unacceptable object for something she is allowed to chew, like a kong, a chew stick, treat, a robust toy, etc.
In the easy form of this exercise, say chewing shoes, when you give your dog the acceptable item you take away the contraband. Enough interations and your dog learns to choose the toy (or whatever) over the shoes.
However, that your pup is doing this to her beds will make the exercise a bit harder - you really don't want to take away her bed.
You might start by establishing the 'swapsies' pattern in another context, trading one toy for another, perhaps. Something easy.
Then having established the basic idea, what I might do with the bed is when you see her start to chew the bed give the interrupt signal, call her to you (to get her out of the bed, a further break from the unwanted action) into a sit, offer the good thing, then send her back to her bed to chew the good thing to her heart's content.
After a many iterations, place the acceptable thing in sight of the bed. When she starts to chew the bed, give her the interrupt signal, send her to the good thing, then back to bed with the good thing.
The idea is that, a few thousand interations of this, ultimately she pairs the good thing with the chewing urge, and makes the choice herself.
Use a clicker to mark whenever your dog makes a good choice, if she is trained to that.
As with any extinction exercise, this takes time, and timing on your part. You have to be there to give the interrupt and further direction so as to establish the acceptable/not acceptable connection.
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I'm a big believer in 'choose your battles'. The Muttley Crew have successfully been trained away from chewing their beds and my duvets/pillows/sofas... but I allow them to rip any toy of theirs to shreds if that brings them joy. All the fluffies have had multiple surgeries to replace amutated limbs, ears, etc.
Obviously I have carefully observed how they shred their toys. None are eaters, they just enjoy the destruction. If there was any danger of eating bits of the toy, I would take a different approach.
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* First you train the interrupt signal, of course. You've probably done this in classes, so it's easiest to use the same signal for anytime you need to interrupt. The signal means 'stop whatever your are doing, look at me' in any and all situations.