She's a bedwetter

Robyn Hill was sleeping one night in her team's base camp when she was suddenly woken up by her second-in-command, May Marigold.

"Robyn, wake up! We need to head out, now!" May said while shaking Robyn.

This only caused Robyn to groan a little as she woke up. "Ugh, what is it?"

"We have reports of one of General Ironwood's weapon shipments being hijacked by an unknown third party, and we don't know what they're planning to do with the cargo! We need to head out as fast as possible!" She explained frantically.

Robyn immediately shot up as she shifted into her leader mentality. "Send some Huntresses to scout the area and give me a location where this shipment is being taken." She ordered, though May blushed a little at Robyn's attire, which Robyn herself soon realized.

Despite being a very stoic person who demanded the truth, Robyn Hill had a very embarrassing secret: She wets the bed and needs to wear diapers every night. It would be one thing if she could change herself, but for all the Grimm she could kill, she never managed to get the tapes on her nighttime diapers right and needed someone like May to help her. "Look, just give me a few minutes to get dressed, and I won't need your help, May."

A few minutes later, Robyn was dressed in her normal attire which she wore on missions, only with her thick nighttime diaper on underneath. Given her bladder was still starting to fill up, Robyn didn't want to risk it in the middle of an important mission like this. "Happy Huntresses, let's move out!"