Vet advice needed ASAP - dog with swollen lip and eye

[kid]

My sisters dog has developed a lump on his lip this evening (10 minutes before the vet closed!)followed a couple of hours later by one eye swelling. She applied ice to his lip which took the swelling down a tiny bit. She gave him 1.5ml of benedryl but that made no difference. He has developed some red spots over his body and is quite sleepy (but thats probably the medicine she gave him). She also commented that he feels quite hot and that his breathing seems a bit slow but not noisy. His pulse is about 60beats p/m.

She is about to phone the emergency vets for advice but I thought I'd ask here too to see if anyone has any ideas or similiar experiences.
Her dog is just over 2 1/2 years old and she is concerned that he didn't have his booster (which was due a couple of months ago)
She is trying not to panic but its clear she is panicking.

I'd really appreciate any advice. I've had a look online but have no idea what I'm looking for really.

(2.5ml of benedryl)

Sounds like an allergic reaction most likely, or possibly he found a bee/wasp? Best to speak with the emergency vet and make a plan though as she is already doing.

I thought it sounded like a wasp sting but she is worried about the swelling of his eye. They did have a wasp nest in their house earlier this year. They couldn't find any wasps in the house today as that was also their first thought.

Not sure what the vet said, she hasn't phoned me back yet.

The vet wasn't overly worried on the phone. He said she could take him in for a steroid injection (£100 to see him plus cost of medication) Or she can monitor him during the night and take him in if he gets worse.
The vets open on Sundays at 10:30 if she needed to go in then.

By 11:30 last night, the swelling had gone down, his eye was normal and he was acting he usual self so no further action was required. It was quite scary though and we are still non the wiser of what actually happened.