Hi
Yes and no. Water flosser is not a treatment option if your gums are sore. You can use it later after healing just to maintain the hygiene.
Your problem seems to be gingival which means infection in the gum. So, the gum needs to heal. Once it heals your dentist can check for any damage to tooth or surrounding bone. ( that can be detected with an x-ray).
Next Steps
Apply topical ointments like Hexigel mixed with mucopain. Just dab it 4-5 times a day on the site and leave it to heal.
Health Tips
Just rinse your mouth with warm saline water twice a day and avoid brushing hard or flossing in that area for a week.