Here's a citation that is exact:
Austen´s indirect criticism of patriarchy is evident in both Emma and Persuasion. Emma loves her father very much but as Austen mentions “He was no companion to her. He could not meet her in conversation, rational and playful” (E 2). He is much older that she is and he is also portrayed as practically invalid. In addition, he is nervous, hating any change and easily depressed. Zuzana Kadlecová, Marriage in the Works of Jane Austen and Mary Wollstonecraft
Here's the citation of the actual line from Emma:
How was she to bear the change? -- It was true that her friend was going only half a mile from them; but Emma was aware that great must be the difference between a Mrs. Weston only half a mile from them, and a Miss Taylor in the house; and with all her advantages, natural and domestic, she was now in great danger of suffering from intellectual solitude. She dearly loved her father, but he was no companion for her. He could not meet her in conversation, rational or playful. (Source: Emma, Jane Austen)
I am guessing that he can't converse with her in rational and playful manner.