I use an old echo park delay pedal on the slap back setting. This type of delay is a common ‘go to’ for a lot of players. ‘Slap back’ is a very short delay, and It’s best used so that it is only just noticeable. There are a lot of delay pedals these days with this setting, it’s very standard. When used right it adds a nice amount of depth and color to the harp.
I’ll then use reverb on the amp, if it has it, or have the sound guy add add a nice plate reverb when playing direct to the Pa with my Dyna-Mic or while recording.