A party around someone else's pool removes the routines that protect your dog at home. You do not control the gate, the cover or who drifts outside with a drink in hand, and your dog does not know where this pool's steps are. Safety here is therefore agreed in advance with your host, practised once on arrival, and then watched over by one person at a time rather than assumed to be everyone's job.
Before the party starts
Ask your host beforehand where the dog can be when she is not swimming, and agree that pool gates stay latched and covers stay on between swims. On arrival, before guests and noise build, walk her round the pool on a lead, guide her into the shallow end if your host allows a swim, and steer her to the steps several times until she turns toward them without prompting. A dog who has only ever entered water at a beach slope may head for the nearest vertical edge here, and that edge gives her no way out. Note also the garden gates and the route to the street: a side gate propped open for guests is her likeliest escape route, not the pool itself.
One watcher, short swims, shut gates
Name one adult as watcher for each stretch, and make the handover spoken rather than assumed — the riskiest moment at a party is when each adult believes another is watching. The watcher stays poolside, keeps her in sight, and calls her out while she is still paddling strongly, because dogs chasing toys or children rarely stop through tiredness. Between swims she rests away from the water with her own drinking bowl, in shade, with the gate shut behind her. Balloons, dropped party food and guests moving in and out add their own distractions around the edge, so keep her collar on and her lead close whenever she is moving between house, garden and pool area.
After a swim
Rinse her coat with clean water once she is done, dry her ears and let her settle somewhere quiet away from the music and games. Watch her over the next hours rather than assuming a cheerful dog is a fine dog: swallowing a large amount of pool water can be followed by coughing, retching, unusual tiredness or unsteady movement. If any of those appear, contact a veterinarian promptly and say how long she was swimming and roughly how much water she may have taken in. Keep party sweets and barbecue scraps out of her reach during this rest period too, since a tired dog left to herself scavenges.
If she slips out during the party
Parties open gates. If she is suddenly missing, check the pool first, then the house, then the street in that order, and send one person to each gate so she cannot slip further while others search. Ask guests leaving on foot to watch pavements and driveways rather than chase her, and keep your phone in your hand. For backup beyond the garden, KinsLe offers the Lost Pet Alert System inside her profile without charge; it appears as a map listing, and enables whoever finds her to contact you by direct message.