No. Dijana shouldn't be going to the Kingdom Hall, nor should anyone here encourage her to. (Though if it were me, I'd take the girls for a one-off Memorial visit just to fuck with Jabba the Hutt and see him melt down on Twitter)
She seems to be supportive of environmental causes and animal rights (particularly whales). It would be quite a bit of a pivot to drop all that and convince yourself that Jehovah is going to take care of all that in due time.
What she should do that would be constructive and beneficial for the girls is working on repairing the damage Lloyd had done to her relationship with her parents. It sounds like they still wanted to be a part of hers and the girls' lives. Lloyd was the one who set all these series of rules for them. No preaching to the girls should be the only rule that is necessary. Perhaps they could provide a vital link between them and their family history, Croatian culture and heritage.
Oh. And please do find a man. It'll be great for her own fulfillment, and she'll find out how it is really like to have sex that doesn't require her partner fluffing himself up to porn prior. The girls might actually have a positive male role model for the first time in their lives.
He'll write and perform a breakup song and it will be EPIC.
So you've taken someone into your life.
Now I know for sure you are not my wife
You've cried and complained when I went to Pa Tong
When all this time I've done nothing wrong
Despite my love you sought someone new
Keep your silence about me or I might just sue.