Its half way all ready in so far as your girlfriend has already been to the UK and presumable complied with her visa conditions so well worth applying again she can aditionaly say that she wants to visit you as well as the family
On your second point vis the tax-man not enough info to comment you have to demonstrate that you can support her initialy but its also possible for example if she was already your wife and had a verifiable job offer in the uk that would help also even if your a bit skint
