Still unable to get a Landscape Designer job, is it better to take a related admin or non-profit job?

I’m not sure anyone can answer that adequately, as both have potential. I think I would try and explore whether the administrative person might occasionally be considered an additional resource person in a crunch. With good supervision, that might help you get a feel for (and a few portfolio samples related to) the technical side of the practice, as well as building some knowledge and confidence. However, be wary that may not happen. In the nonprofit, networking is a benefit but moving into design will still come down eventually to having something to show in interviews. Again, could they allow you to come up with preliminary concepts or illustrations? I’m doubtful that avenue will be as technical but it may be the prospect which actually makes an offer. 

You said it better than I did…. I wondered a bit if it could be a limiting pigeonhole in the wrong firm but on the other hand, they know what her background is coming in and must be interested. It’s bound to occur to somebody there, now or later, this would be a built-in way around the hassle of hiring outside temporary contractors, or overburdening other staff. Maybe even if it had to be extra hours? There’s the hazard of being asked to carry more than a fair load (admin. set to the side but still expected at same level). But that’s a hazard anyway, anywhere you try out.