If your other cat is an unneutered male, then he's just contributing even more to the unwanted pet population.

Cat neuters these days run from $30 to free(I've done TONS of Nickel Neuter days). There's no reason to not have him neutered.

She'll gain alot more weight and be much healthier if you get her on a name-brand kitten food. They eat alot less, poop less, poop doesn't smell near as bad, and they won't have irritable bowel problems. Try at least Purina One kitten food. You'll be surprised.