I haven't kept otos, mostly because their sensitivity scares me. Most are wild caught and generally don't accept commercial food. Hopefully the otos accept the zucchini and/or spinach, but if not, she may need to grow some algae. I think this blog is a good read on otos and here's an excerpt on growing algae:
http://www.myaquariumclub.com/before-you-buy-otos-please-read-this-8507.html
"I do a couple of things to try to make sure my Otos eat as well as possible. One trick I use is keeping a lot of small rocks in large jars of water, which I leave under the strongest possible lighting for a minimum of 16 hours a day and preferably 24/7. Direct sunlight works too, if you live in warm enough place. I feed the jars with some fertilizer which is made to grow algae specifically but any fertilizer used to grow plants in a fish tank would likely do as well. The water in the jars comes from tank water changes and is also used to top them up.
I have found that marble chips and ceramic filter media seem to grow the most algae in the least amount of time. Some other rocks work too, so long as they are not polished. If a rock isn't turning green, just take it out. I drop a few green rocks in the tank at each end, then return them to the jars when they're clean. My Malaysian Trumpet and Rabbit snails appear to adore the rock algae too and will swarm a new rock in minutes. I have to make sure there are enough rocks so the Otos get their share."