Red footed tortoise eat shadow bennie

Hello, I'm wondering if my red footed tortoise can eat a herb called "shadow bennie"? It's got a lot of different names, but the scientific name is Eryngium Foetidum. I'm new to red-footed tortoises (any tortoise actually), and just started fostering one.

Also, what's the minimum size enclosure she would be comfortable in? She's a year old right now, and in temporary housing until I can find her something bigger. I don't really have access to pet stores here, so I'm looking for large storage containers - does that sound ok? And is a calcium supplement mandatory, because they don't have any at the tiny pet store near me :( Can I supply her calcium another way?
Sorry for all the questions, I really appreciate your help!