1人分 here does mean "one person's portion", and in this context it refers to one person's worth of living expenses, i.e., the living cost of アンタ, which the speaker thinks is small enough.
And do you understand what 回せる means here, which is critical to catch the meaning of 1人分? This 回せる is the potential form of 回す, which has a slangy meaning "to manage", "to moderate (party, etc)", "to run (shop, etc)", "to keep going", etc. (Surprisingly, this meaning is not in jisho.org.) In this context 回す means financially making ends meet and keeping the family together.
It's just one person's worth (of living expenses), I can make ends meet (only) with my wage!
I can at least afford one person's worth (of living expenses) with my income!