Swelling of the behind area

My Jack Russell Terrier is 9 months old and recently I've noticed a change in her behavior (not bad) -just more submissive and loving, but I've also noticed a slight swelling of her whole behind area. Could this maybe be due to her first coming into heat or do you think that it could be something else?

She has had problems with scooting-- anal problems before but I thought the anal glands was right by the anal and would not cause a slight swelling of the whole behind region--below her tail.

Could it be a bowel problem--with no other symptom as I have read about in other Jack Russel Terriers.