The second idea for helping you to tune to the piano I call The Swoop.

Have the pianist sustain the note A. (You can do this yourself using the sustain pedal). Play your flute A along with the sustaining piano A but then stop your flute sound and listen carefully to the piano note. Did you feel the pitch moved up, or swooped up to the piano pitch? If so, then your flute note is flat and you need to push in.

If when you stop your flute note you feel the pitch sag down to the piano pitch then you are sharp and you need to pull out.

When you are in tune with the piano, once you stop your flute note there will be no movement of the pitch either up or down to the piano note. They match!