Let the lab tell her when he's had enough... she'll soon get the message.
He doesnt though. He's too gentle and playful himself.
he will, after it goes on for a few days... try it and see on a weekend...
Jock lab (7 yrs) and Fern working cocker (11 months) play fight, Jock still hasn't told her off to this day, he just gives into her ALL the time when he's had enough he just goes off to his bed and keeps out of her way - she never stops
I have Sapphi, 3 yr old working lab and Barney, 9 months old cocker plus Max, 19 mth Golden Ret. Very similar story, Sapphi never told Max off when as a pup he hung of her ears, stole everything from her, humped her, chewed any part of her he could get in his mouth and rolled around together. She still hasn't.
When we got Barney she wasn't that thrilled to begin with, but now puts up with all the things she did from Max.
Max always put up with Barney's antics as a young pup and although Max is the boss he's never put anyone in their place, he's very quietly the boss.
All three play fight, usually in an evening when I'm watching TV.
To me its just part of the joys of owning more than one dog. I do have a "quit it" command if its getting particularly noisy. I love to see them interact with each other.
Personally I think you should let them be together, the more you seperate them and keep them apart the longer this will go on as there will always be the novelty factor when they are allowed to be together. Get a crate for your pup and then let them sleep in the same room. As you quite rightly point out a lab is much bigger than a cocker pup and accidents can happen but carefully supervised they should be fine, if you can't supervise pop her in the crate.
This is all part and parcel of owning a pup and an older dog. Like others have said sleep and TV don't feature much when you've got a young pup in the house.