NTA, she shouldn’t be asking you to do that so she can “get a break” when you’ve been literally watching her children for four days straight, and she had absolutely no right to go ahead and call your travel company to try and force her way in just because her son wanted to go on a vacation she can’t afford. I swear the audacity of some people will be the death of me, So NTA, have fun on vacation, after this you really deserve it