Welcome, and how sweet of you both to rescue this poor girl.
Well, if she doesn't have any immediate injuries that require attention, I think I'd just give her a bit of time to settle in, gain some strength and feel better about herself, though it sounds like having people, food and a wonderful/safe place to rest/sleep is like Heaven for her. As for grooming, I wouldn't. When she feels better, she will groom herself. You can *help* her by using a warm/damp washrag, gently running and scrumbling it over her dirty fur. Food and water seemed to have been in short supply for her, and what she is eating/drinking now, is going to nourish her body. She will create 'waste' material after her body's immediate needs have been met. It can take 1-2 days before a starved/dehydrated cat will eliminate any waste.
As for fleas, I would use a spot-on treatment, Revolution, Advantage, Advocate or Frontline, available at vets offices, pet stores or mail-order catalogs. Give her a chance to gain some strength, first. These meds usually just affect the bugs, but if a cat is *very* weakened it could affect them, too. I would also advise a vet visit for spay confirmation and vaccinations in conjunction with a general exam to see if they can help her with her other injuries (tail, bumps, leg-limping) and do their best to make her comfortable.
She's a very lucky kitty she fell into the hands of two compassionate people. I luv ya both!