She's chomping on too many of her own people--most who have superior fighting (Morgan), weapons (Sasha) or general technical skills (Eugene), so that's something to consider, since she's fond of judging the value of others. In fact, the Alexandria residents should be flaming mad at her, as it was clear her botched attempt to kill Negan led to Oliva's murder.
Everyone has been through trauma and loss in the ZA world, but most did not walk around being a complete ass to those who did not deserve it.
It just may be how she "reacts" to stress, particularly when she blames herself (she's responsible for Eugene being captured as she forced him to make the bullet) couple that with the grief over the relationship ending with Abraham, Abraham's death and now the death of Spencer and the "relationship" budding there she's just putting up an offensive shield to deal with her emotions. It's how some people react to blaming their-self the over-react on others.
She's got little reason to mistrust Father Gabriel, particularly after the talk they had in the previous episode, but she's biting out and not thinking rationally.
Yeah, Oceanside residents live in hiding and rarely move out that far. Contrary to some viewers, this new group is not all female. Whether or not they're the Whisperers is another matter.
I don't think they're The Whisperers, this would be "too soon" for them to appear (if the show traces the comics even as tangentially as it does), this isn't how the meeting goes in the comics and their presentation here wouldn't align with The Whisperers in the comics. I think they're an original "new" group to the series.
How is she being childish? She has suffered enough that she does not want to be involved anymore. While the series might have her break that desire to avoid fighting...and end up being killed (more than a few rumors about that), one can understand why she does not want yet another round of fighting psychopaths.
Because there's almost no reason for her to behave this way and to want to isolate herself in this manner particularly to people she's known and been close to for the last three years (particularly Rick and Daryl.)
But, for me, her switch to this mode is almost as sudden, "out of character" and random as her switch to bad-ass woman who can aim bottle-rockets at propane tanks.
In Season 3 she nearly shoots Rick in the foot after sniping at walkers in the prison yard (this being the better part of 10 months into the apocalypse and been on the run the whole Winter) and holds up in a prison closet for a couple days freaked out after the prison "walker riot" where Lori died.
Flash to Season 4, a few months later, and she's a bad-ass killer teaching kids about guns in "school" and going around stealthily killing people at Terminus.
Season 5, she's this hard-ass liar and manipulator, tough-talking to children and then Season 6 she's again the elite killer with the Wolf Pack.
Now she's dealing with some-kind-of killer PTSD where she wants to be left alone and not kill anymore? It just seems like a sudden turn around after 3 seasons of her emotionless-ly killing people and wanting to kill people who are threats (like the Wolves and the Wolf Morgan captured. And, yeah, she struggled killing Lizzie and it obviously messed with her but it didn't seem to impact her too bad as right afterwards she's easily killing the Termites and threatening to feed a kid to walkers.)
It's out of nowhere.
But, along the same lines, Morgan needs to "grow up" too with the pacifist bullshit. He's seen how The Saviors operate and he found out they killed four Alexandrians/of "The Group." He may not have known Glenn and Abraham that much but he certainly should have gleamed what a good-guy Glenn was just from talk to him a bit and hearing about him from the others. So he shouldn't so quickly be "maybe we can work out a peace without a battle." He should realize the problem The Saviors are and be off the pacifist nonsense.
) especially with Rick and Michonne with the trip-wire and the walker herd. Sort of made me think of "Ghost Ship" though, granted, the wire scene in that movie was a bit different. 
