Girl won't come out, or isn't sure about you… or you're too busy to meet her 1-on-1? Extend a group invite date to her, and get her doing something social with you.
My normal advice with you for dates is 'get her out alone with you'.
Don't make dates less intimate. Don't do party dates. Don't do things where there are other people around to distract.
In the typical scenario, where you have a girl who's already game to come out with you 1-on-1, this is the best advice for you. There's no need to overcomplicate things for yourself or introduce chaos by involving additional people. Make the date about you and her, and get everything else out of the way.
However... there are a few scenarios in which 'get her out 1-on-1' isn't practical or viable. And sometimes it just makes more sense to do something in a group.
For such cases, it can actually make sense to skip the 1-on-1, and invite a girl to a group event.
Because just like 1-on-1 dates, group invite dates have their upsides, too.