Ok so step mom dilemma

I'm a step mom. we have the child 50% or the time if not more. mom still gets child support that hasn't been modified since the new 50/50 agreement over 2 years ago(state is dragging it out or not even trying to modify it). well mom has 50% custody but only spends about about a 3rd of the month with her kids or less by choice not because of work. anyways she signed up to go to Indonesia for a mission trip to help kids in orphanages for a month. Idk but am I the only one thinking it's weird that she somehow has the money for a $3000 trip plus more for the stay but gets child support every month ($400)and only spends about at most 6 days a month with her kids and complains she has no money and how is it she can take the time off from her job when she is always in trouble with losing her job conveniently when the kids need to go to the dr(or when she is at the gym and not at work and says she is at work). also why is it she can take a month to spend with other kids but can't even take care of her own kids. I support her doing it because it is for a good cause but really it's a bit hypocritical to be doing this for other kids when she ignores her owns kids on a daily basis and does nothing for them. once again she is disappointing her her own child and I have to be there to pick up the pieces of a child who is heartbroken over her own mother choosing everyone else over her. It just makes me sick to my stomach to see that her mom is only doing it to look good all the while her own child is suffering due to her absence by choice all the time.