A bacterial infection is caused by.. bacteria. If they penetrate the body's defences and multiply they can cause an infection. Her White Blood Cell (WBC) count is up because these are the cells that fight off an infection. This is a good thing at the moment. I would imagine that her temperature is up, and this would cause her heart to beat more quickly. It is possible that she has contracted this through contact with the dogs eg, ingested something that the dog has brought in (dirt, faeces, etc) but there are many possible sources of infection so it is best to not jump to conclusions. I assume the tests they are running is to find out the type of bacteria involved. This may give clues as to possible sources of infection. The treatment they will administer is most likely to be antibiotics. These will kill the bacteria causing the infection and your housemates daughter should recover. If your friend is worried, advise them to ask the hospital staff.