I've never flown before (too scared to do so), but I feel like there's ways she (and anyone really) could've gone about it differently besides just making a post on social media. If she didn't want to tolerate it (which is certainly an option, though one she doesn't need to feel compelled to take!), then she could've politely asked the men to move their legs over (or even switch seats with her, if that's an option on flights). If she felt uncomfortable speaking to the men directly for whatever reason, she could've spoke to a flight attendant. Maybe arrangements could've been made to move her seat somewhere else where it wouldn't have been an issue. It doesn't have to cause a scene unless it's turned into a dramatic issue. Just simply asking politely and empathizing with the other person while also acknowledging your own discomfort can go a long way. Even if the three of them couldn't work something out among each other, I'm sure the flight staff could've helped them out and figured out a way to allow the men to have their space while allowing her to be comfortable too, assuming the men couldn't simply close their legs a little bit for the duration of the short flight.
I've taken public transit quite a few times over the years because it's been a more convenient option compared to driving to an event myself. Every time, without fail, I'll end up having to stand on the light rail ride back to our station that we parked at (I'll let my mom or someone else have a seat because I'm more willing and able to stand), or I'll have people leaning over me because they pack the trains on the return trip after big events. Is it uncomfortable? Yeah, absolutely. What have I started doing? Going on a train in the opposite direction or chillin' in the immediate area for about 30 minutes to an hour while they clear out the bulk of the crowds, then getting on a train back after everything has died down. Don't have to deal with an overcrowded train with people on top of me, and I have a guaranteed seat, and all I have to do is be mindful of the schedule to ensure I'm at the nearest station in time for the last train back home. Obviously not an option on flights since you don't have the option to simply switch flights because one's overcrowded or you're in an uncomfortable position, but the moral of the story is there's ways to work around it.
Couldn't the guy on the aisle seat just spread his legs out that way?
It's possible, but I think then you run into a safety issue. If he or someone walking by isn't paying attention and his legs get tripped over because they're in the aisle, it could become a problem for the flight staff, who will inevitably have to deal with the incident.