My girlfriend had hernia repair surgery at the end of july and now she has a soft lump on her abdomen. The lump is most noticable when she is laying?

Sounds like a seroma. The body is designed to fill up empty spaces with fluid; when these develop in an area under a scar after surgery, we call them seromas. This is especially common after hernia repair with mesh.In time, the body absorbs this fluid. If it persists for more than 6 months, needle aspiration may be necessary.These may be difficult to distinguish from a recurrent hernia, so surgical follow-up is a must!
Seroma vs Recurrence. Often times after a hernia surgery people will get a seroma. It is best to leave these alone unless they are vey painful. They will usually resolve in 3-6mo. If still present you need to consider a recurrence of the hernia. Best way to DX is by physical exam by doctor. May also need a CT scan or Ultrasound.