We can also see the sign for Myrddin Davies, Cash Chemist. It also appears that there is a bit of horse manure on the right side of the road.
Perhaps the young girl is shielding her nose from the smell.
Here's the back of the card, sent to Mrs. C.E. Potter of Potter, Kansas in 1926, with the following message:
This from the ____ lady on the train returning from ______.
We had a most delightful voyage across - seven days on the ocean blue - It was grand -Will be traveling to Scotland + France before we return Sept 25th date of returning sail.
Fraternally - Mrs Evan Davis
The recipient of the card was likely Charlotte Estelle Potter.
It's worth noting that the post office in Potter, Kansas opened in 1865. It was threatened with closure back in the 1970s, but didn't actually close until 2009. In 1976, Wendall Anschutz filmed a travelogue piece on Potter and its post office.