the hard drudgery of real practice

OED:

practice, 2.a. The actual application or use of an idea, belief, or method, as opposed to the theory or principles of it; performance, execution, achievement; working, operation;

1969 D. Cairns tr. E. G. A. Husserl Formal & Transcendental Logic 32 The distinction is after all a relative one; because even purely theoretical activity is indeed activity—that is to say, a practice.

2002 RAF News 25 Oct. 25/2 (advt.) The College..has developed a 2-year web-supported distance learning course which integrates theory with practice.

'Practice' has a number of definitions but the most relevant of those offered by the OED at Lexico in this contexet is:

The carrying out or exercise of a profession, especially that of a doctor or lawyer.

In Eliot's case she was referring to the 'profession' of novel writing and the rigorous work required to make a proper job of it rather than the much easier task of writing what we would now call 'trashy' novels.

Eliot was, and very much considered herself to be, a serious novelist producing work of real quality. In this passage she was contrasting such literary work with the much inferior work produced by other women, often as a hobby rather than any real commitment to the art.

She obviously considered such pieces of writing to be completely divorced from the work she and other serious novelists were producing and wanted to encourage other women to take the art and craft of novel writing seriously and analytically rather than using 'feminine intuition' to produce inferior work.

You should note that 'pracitce' in this context is not used in the sense of

Repeated exercise in or performance of an activity or skill so as to acquire or maintain proficiency in it.

which is more familiar to many people.