The meaning of “hard” in this sentence

"Hard" here is an adverb, meaning "with a great deal of effort".

Use it in a sentence, "I work so hard to get this job".

The first part of your sentence can be reshaped to "the control and discipline came to me with a great deal of effort".

Note that all the above holds valid unless "came" plays as a copula, also known as a linking verb, which shows a transfer of physical or mental state, meaning "became". It is instead an adjective. This uncertainty, however, merely bring few to no difference in the meaning.

In this sentence, using the word "hard" means that certain aspects of mothering (self-control and discipline) presented themselves as difficult to the narrator.