Apart from the lump which hopefully Arnica will help, you could look at 3 other areas.
1) For the inflamed gums and bad breath try Merc Sol 30C twice daily for 3 days. If the teeth have a lot of tartar they may need properly descaling but you can patiently pick at it with your fingernail every time she'll let you. If they are not too bad try using a doggy toothbrush and toothpaste gently and reularly. (They may bleed at first but don't worry)
2) For the snorting and nose discharge that's maybe causing this, the Merc Sol may help. You may though have to use another remedy, perhaps Pulsatilla etc later.
3) For the gassiness, it could be that she needs some changes in her diet. It's difficult to advise, but you could try more plant roughage in her diet by giving some vegetables. If you make one small change at a time and observe for a few days, you can find what suits her