Lump On My Groin Under My Stomach My Boyfriend's Dog Has A Hard Lump In Her Stomach/groin Region. Does Anyone Know What It Could Be?

My boyfriend's dog has a hard lump in her stomach/groin region. Does anyone know what it could be? - lump on my groin under my stomach

We took them swimming a few days ago and was even working too hard, I think it could be a hernia, but I'm not sure if she wants to dismiss more serious. We can not today see the vet, so I wanted opinions on what could collect. It's only a couple of really strong, near the bar on one of her nipples. At first we thought that she was pregnant, but only on one side and is very difficult. Ideas? I think it will be ok?