Thanks for asking! It’s a truism that every group officer would like to be kept in the loop about events, even moreso when that officer will later get blamed if they’re seen to be not doing their job. This is particularly true of heralds, who risk raising the ire of heavy fighters if they don’t show up when they’re needed!
In general, you can assume that if your local branch's herald shows up to an SCA event, she will be planning to take charge of whatever heraldy things are needed at that event. "Take charge" in this context may simply mean the same as "ask someone else to do it", but regardless you can assume a herald at an event is there in an official capacity.
What you can't assume - and this is a trap a lot of feast stewards fall into - is that the local herald will attend every event. If your local herald has an attack of Life or some other commitment, or just doesn't feel like trekking all the way to an event a million miles from her warm living room, then you're out of luck.
So you need to call the local herald well in advance of your event and make sure she's planning to get there. If she can't make that commitment, she's obliged to find another herald for you, because that's part of being the local branch's official representative of the College of Heralds. But if you don't ask, nobody will necessarily think of it for you.
So: simple problem, simple solution. Communicate with your herald! While you're at it, communicate with your marshal, hospitaller, chandler, chirurgeon, constable and seneschal. Let them know what's happening, and make sure they're informed. It's part of your job as steward, and it's not too tricky. Better than the washing up, anyhow.
Author: Karl Faustus von Aachen. Updated: 15 May 2009 (AS XLIV).