That's Lasius fuliginosus, the carton making jet ant. Really fascinating species.
The ladybird did seem frustrated with the whole ordeal.
I don't think the outlook is good for the aphid as it's injured... ants will snack on the herd... but it's interesting that the ants noticed that the ladybug was eating ... rather than just having a vague instinct to chase away any creature that is on "their" tree near "their" aphids.