Charms are definitely possible. Specifically making you tougher might be difficult, but if I can find some suitable components a luck charm would work perfectly for making it easier to avoid being hit.

[Also not a perfect solution, but it would definitely help.

Ruby is also finding it a bit weird and unexpected to realize that she's actually enjoying genuinely coming up with the right solution and spell to use, rather than manipulating the situation for her own gain. Sure, she's still keeping in mind what's not going to backfire on her, but it isn't the only thought on her mind and that's odd to realize.]