She was thinking of Spinoza's kind of striving, conatus

The importance of Marx in this connection is that, no doubt for the first time since Spinoza’s conatus (‘effort’), the question of historicity (or of the ‘differential’ of the movement, instability and tension within the present which are carrying it towards its own transformation) is posed in the element of practice

Spinoza calls ‘conatus’ the effort by which ‘each thing, as far as it can by its own power, strives to persevere in its being.’