Not every cry for help is a cry for help, sometimes its a bid for connection.
But is validating her feelings the only thing I can do?
its easy to validate the complaint (yeah they are evil people for doing that to you), but what's under the sensitivity to "the smallest things"?
why does she's feel attacked/neglected? what need does that step over, leaving her abandoned and desperately trying to get someone else (you) involved?
validating the deeper need, understanding what she can't put into words and just "gets it out" by bad mouthing others, is probably the goal here I think.
Is there something in common about these "little things" that you can notice? you mention it being about family members, is it always about people or are "fun weekend" things/events/mishaps also a target?