‘Looking at the song I have to send, the RMS is about -17db and there are a handful of peaks that go above -2db. Some reach -1.3dB. Should I have everything lower than -6db before sending to you?’
No need to overthink it.
If that’s all as it should be then export to a 24-bit wav/aiff file, at whatever sample rate the track was mixed at (avoid sample rate conversions please).
Simple as that.