There is a huge tendency to over diagnose on the internet.
When she says she feels her sugar Levels drop and feels dizzy it's a big leap to being diabetic. Could be a range of things. Drinking juice on a 4 mile run is an indication that your understanding of your nutritional needs are wrong.
Cut out all juice and dizzy drinks and any Lucozade type 'sports' drinks you might be drinking as well.
See what happens before rushing to the doctors for a diabetes diagnosis.