why did geillis duncan save claire at the witch trial?

I read the books and I am rewatching the series for the second time from the beginning (and wow, crazy how season 1 is sooooo much better than season 5-8).

anyways. the character of guillis is the one that i cannot figure out.

in season 1 she pretends to be a friend, but is she really? i always doubted her motives.

but at the witch trial she really does something selfless, she saves claire. why?