Depending on who's giving the shower, it's not unusual around here for the mother of the bride (& the mother of the groom) to be given corsages in addition to the bride.
Since the shower is in August & at someone's home, I think capris would be fine & wouldn't necessarily be inappropriate - as long as they are dressier & paired w/ a nicer top. Instead of capris, which I think of normally hitting just below the knees, a pair of cropped pants might work better w/ a nice pair of sandals. To me, cropped pants look dressier than capris.
A summer dress would also be nice - I'm thinking a sleeveless linen sheath dress maybe?
What is your daughter wearing? Also, who is giving the shower? Are the shower hostesses typically more casual & informal? Is this going to be a formal shower or a more casual get together? In my "circle," I've been to very informal showers in homes, where the mother of the bride was dressed very casually - capris & a nice top would be perfectly fine & even expected. I've also been to dressier & more formal showers in homes where the mother of the bride was more "dressed."