There's no limit. As long as she has the connecting boarding pass and doesn't leave the lounge (the passes are one-time, not one-day), there should be no problem. There's no limit.

At United Club locations, there is generally no strict "hourly limit" on how long you can stay, provided you have a valid same-day boarding pass for a United or Star Alliance flight. Most travelers use the lounge for 2 to 3 hours before their departure. However, you are typically only allowed to enter the lounge up to 3 hours before your scheduled flight time at your departure airport. If you are at a connecting airport, you can stay for the entire duration of your layover, even if it is 6 or 8 hours. For the premium United Polaris Lounges, access is also granted upon arrival for international travelers, but you must have a confirmed onward connection. During times of extreme overcrowding in 2026, lounge staff may implement a "capacity management" policy, but as long as you have a confirmed seat on a departing flight, you are welcome to stay until your boarding group is called.