Conveniently, how
accepts a list:
df1 = df.resample(rule='1D', how=['mean', 'count'])
This will return a DataFrame with a MultiIndex column: one level for 'A' and another level for 'mean' and 'count'. To get a simple DataFrame like the desired output in your question, you can drop the extra level like df1.columns = df1.columns.droplevel(0)
or, better, you can do your resampling on df['A']
instead of df
.