Hi there
It's a bit of an odd circumstance and I'm not sure whether you should do this. Reciprocal links can look suspicious to search engines, but putting aside that issue for the moment, let's look at the SEO impact.
If you link to the site from your own website, it shouldn't effect your rankings. If the site is high authority as you say it won't be a problem. Problems can occur when your website is linking out to spammy or penalised domains, but this shouldn't be the case here.
If you're planning on linking to the site, I'd advise you to do so in the most contextual way possible, to avoid it looking like a link designed to pass PageRank (which, really, it is - hence my hesitance to say "go for it"). If you can reference the non-profit organisation, highlight who they are, what they do and how you two have collaborated together on projects, then you're reciprocal link should look A-OK.
It's an odd one because I'd always advise not to create or earn links for the sole purpose of passing PageRank or SEO value. On the face of it, this is what it looks like. But if you consider that your link may help to boost the site in the rankings and in turn your referral traffic, which is a considerable amount of your business, I can certainly see the reasoning, put it that way.
What I'd say is that if you're going to do it, do it right and just as you would when creating any content. Give detail, user value and pull on the experience you've had together. It might end up being a piece of content that goes a long way towards building legitimacy and brand trust, which would be great. I'd also add that your link may not be enough to improve the ranking of the site, which means its all the more reason to make sure it looks like a real bit of content.
Hope this helps