@WM-R  
XD
 
Or, Sweets and Apple blindfolded her and surprised her.

@Background Pony #CD90
 
That, or she climbed in during a song when she wasn’t paying attention.

@WM-R  
So… Scoots just got in to the cannon on a dare or something?

@Background Pony #CD90
 
The CMC weren’t the sharpest knives in the drawer in those days…

XD Scoots face in the first panel is priceless!
 
Only one question, how did they get her in the cannon without explaining what was going to happen?

@vonPeterhof
 
Ah, when you put it that way…
 
But on the other hand (hoof?) the fact that Sweetie and Applebloom are all teary-eyed makes me think that the “if” translation would work better in an “we don’t think you’re going to make it, but we’re doing it anyway” kind of way.
 
In that case, Scootaloo’s “flag” line is more of a, “I’m going to make a sacrifice, so let’s make a promise that probably won’t be fulfilled” situation. Which is still a death flag, just a slightly different meaning than the one you put forward.
 
But like you said, it boils down to personal preference.

@WM-R  
The ~~tara is actually a bit ambiguous in that it can mean both “if” and “when” (it always means the latter when talking about events in the past). Personally I think the “when” translation works better in a “tempting fate” sort of way, leading into Scootaloo’s “flag” line ~~ a character expressing certainty about a happy future event with another character signals to the audience that the latter character isn’t gonna make it, hence “death flag”.

@vonPeterhof  
I think the ‘Let’s do more crusading together when you come back’ is more accurately ‘Let’s do more crusading together IF you get back, okay?’, followed by ‘It’s a promise’.
 
The ‘-tara’ (as in kaettara) modifier is generally used to mean if, if I recall correctly.
 
Plus it makes Scootaloo’s reaction a lot more hilarious. “Whaddaya mean IF?!”

Translation:
 
“Fried chicken!?
 
S: um… You guys? Would you kindly explain this situation for me?  
AB&SB: we came up with a method to make you, who can’t fly even though you’re a Pegasus, fly!  
S: y-you’re kidding, right!?  
AB&SB: let’s do more crusading together when you come back… It’s a promise…  
S: hey, don’t raise weird flags!!!  
AB&SB: okay, okay♪ well then…  
S: this isn’t funny!! Get me out if heeeeeere!!!  
AB&SB: have a safe flight⭐️  
Nice weather  
Isn’t it?”