Some sort of allergic reaction?

My friend has just rescued a 16 month old GSD ( ) and the second day he had her, after she got back from her walk she started acting strangely. Rubbing herself on the floor and whining and being a bit distressed. He phoned the vet and the vet suggested Piriton as it sounded like she was irritated by something.

She had also been in/near a rapeseed oil field and I believe some dogs have allergies to that, so my friend was going to stay clear of them.

Today she has just come back from a walk in some grassy fields and has had a reaction again, but he said the piriton has stopped it so he isn't sure if it's her paws or face or what exactly is bothering her....

She is a failed police dog and has spent a lot of her life at the police kennels so I think she has been used to a grass field, but maybe not much else.

She is such a gorgeous girl, does anyone have any ideas what could be bothering her?

Toby has had nettle stings a couple of times but you'd probably see the lumps if it was that?