What is LE (plant contents)?
My answer will unfortunately have almost nothing to do with chemistry.
The quoted statement is BS, there's no vitamin LE.
This claim appears to appear on several web pages, the common source seems to be a post from an nutrition/herbal oriented mailing list from 1998:[1]

…
OATSTRAW
Oatstraw as any livestock breeder will confirm, builds the strongest possible
body, with the greatest resilience. Used extensively in European cultures
throughout time for health and beauty, our country has let this valuable herb
slide into disuse.
Contains: calcium. high in Vitamins A, C, B complex, LE, G, phosphorus,
potassium, proteins.
Oatstraw contains Avenin, an amorphous alkaloid which is highly nutritive to
cells, improving normal cellular reproduction.
…

(also note e.g. that avenin is not an alkaloid but protein)
I have an evolution theory how the author could have made this typo, when (hopefully) compiling a literature:

… vitamins A, B complex, C, E, …
… vitamins A, B complex, C E, …
… vitamins A, B complex, CE, …
… vitamins A, B complex, LE, …
… vitamins A, C, B complex, LE, …

(Some intermediate forms might be purely hypothetical. An intermediate form “… vitamins A, B complex, C E, …” can be seen alive at the page mentioning oatstraw, at a different product though[2])
References:

http://www.geocities.ws/chdigest/herbs/pages/apr1998
https://www.healthylife-solutions.com/blog/2017/5/15/womens-herbal-tea-recipe