There is only you who really knows your situation, if you feel you could include her in your brood whilst still giving your original cats a good home then I say go for it!
She sounds like she needs someone to care for her and if the introductions go ok then one more can't make that much difference.
Maybe if you had like 20 then it would be a bit much!

I would like more than my two house cats but I am forbidden (miserable OH!)