I'm glad she's doing little better.
You've been traveling with them correct?
Temperature changes as well as altitude?
I'd try to keep her somewhat warm if possible. Around 65-70 would be good.
For the Vitamin E, 450mg is 1000IU so you I would aim for half which would be +/- 500IU.
I would take a "known" like 1tsp coconut oil, canned cat food, liverwurst, yogurt, etc.
Prick the gel cap and squeeze the contents (sticky oil) into the known (1tsp) of your choice. Mix well. Then give 1/2 of your mixture today, then the other 1/2 tomorrow, repeat daily as needed.
Make sense?
If not, then I'd give the whole tablet once every other day. I think short term the 1000UI wouldn't be too bad, some double up on the 400UI for several days at the beginning of treatment, but I would not give for more than 10 days in a row at the 1000IU. Or that's my opinion of what I would do.
Altitude Sickness. Does she have any fluid (Ascites)? If so, do you have any Aloe Detox?
@coach723 uses that to help with Ascites. I saw on Poultry DVM there are a few herbs that may help as well.
https://poultrydvm.com/herbs.php
@LaFleche may also have some thoughts on how to address symptoms more naturally too.