Given you've diagnosed her as negative the challenge is going to be taking her criticism with a grain of salt. I get it too, my GF is very negative and risk sensitive. I try to just accept that and see it for what it is instead of getting bummed out by it.
You never wanna be so high on your own supply that you ignore the rammifications. You do however want to be rationally optimistic and have the growth mindset of putting in the work. The most successful entrepeneurs seek out harsh criticism as an important counter-balance to their beliefs so they know the cons as well as the pros.
If you can find a way to learn to accept criticism as the "con" POV then it will be valuable. If you're too early in the process and the negativity will hurt you then you should probably just not discuss it with her.
Congrats on taking the leap!
My advice is to view this as a marathon. Don't let the gnawing pain of uncertainty, fear, anxiety, doubt and loneliness discourage you, just stick to your mission. Focus on your goal and don't stress too much about the bank balance!