Does this mean that she will eat soon?
It means that she eats very (very) quickly.
Oh, that sounds like me, blushes. Haha
That would be
היא אוכלת בעוד שניה
why "bishniyah" and not "beshniyah"
Because the "sh" sound doesn't have a vowel.
Excuse-me, I didn't understand your answer ? What does it mean that this sound doesn't have a vowel ?
The "sh" is part of a larger syllable "shni". The vowel of the syllable belongs to the "n" consonant, not the "sh".
And the rule is that the letters ב,כ,ל get a khirik (the ee sound) if they come before a letter without a vowel
I'll just add to the correct answers here that in spoken Hebrew everybody say /beshniya/