I have a 6 month old Rottie , She has been crate trained and happy since about 10 weeks . Cage is large enough  favourite toys , treats etc . About 10 days ago she suddenly decided she doesn't like it . It is causing her distress to the point she is drooling so much everything is wet , her feet , ears , bedding and floor . This is breaking my heart . Please help . Any suggestions greatly received .

I would guess that something's upset her when she was in there. Personally I'd leave the door open so that she can choose to go in there or not.

I leave the crate door open during the day when we are home so she can come and go . But when we go out we need to be able to close the door , my house is open plan so I don't want her wandering in case of destruction . I did think that something scared her but we cant seem to move on from that

I would try moving the crate to a different position, preferably a different room and change it's set up. Ie different position, new bed, cover cage with a blanket and leave the door open and see if she is happier. If something has upset her which she is connecting with the crate hopefully it will help to break the association. How long are you expecting her to be shut in the crate every day?

We only leave her for 3 hrs . She is taken out for a walk before hand . We have changed her crate and bedding already hoping that would work .Up until about 10 days ago she was sleeping in there all night , now she gets instantly distressed

What about trying to make it a happy place for her? Start feeding her in it, give her a tasty stuffed Kong in it so she makes the connection its a nice place.

How have you changed it? just wondering if there is anything else to try in that way.
couple of q's: Did she go in freely without you shutting her in before this? Does she ever go in it without asking now? where in your house is the crate?

I hope you can get to the bottom of this but I would say though that for now if she is that stressed then forcing her is going to make it much worse. Do you have a room you could puppy proof and leave her in instead for now whilst you go back to basics with crate training without having to close the door? like the bathroom or utility maybe?

It is causing her distress to the point she is drooling so much everything is wet , her feet , ears , bedding and floor

I think your dog is spelling out, in the only way she as a dog can, what not to do, I cannot make any constructive comment beyond that.
.