My 6 month boston did that this morning. She was licking her lips then dry heaved some little foam but she did not pass out she just licked her lips and smelt around after like nothing happened. Then she had dinner and has been normall all day.

My boston has never puked up until last tuesday when she was spayed. Later that night she puked. Today was the first time since then. Hopefully it will subside.

Maybe it could be the ventilation near her crate? My pup usually sleeps under the blankets and sometimes it gets stuffy, that plus increased temperatures of spring maybe made her a little nauseous from the heat.

Maybe try keeping the crate away any sort of sun/heat source and add a little breeze from a fan if it's hot?