Have you had her urine tested at the vet? Since she is urinating so frequently I would first rule out a UTI. Is she spayed? Is she sqatting like a normal pee when she does this, or is she jumping around and the pee is just coming out?
It does sound like she is just excited to see her weekend family
. Can you put the dogs in the yard to tire her out and let her get the pee out when you first get there? Boxers can be very hyper and excitable. How much exercise does she get? I think with proper exercise it's probably something she'll grow out of as she matures.