Is a little breastmilk better than none?

So my daughter is 6 months old and wasn't gaining weight like they wanted so I have to supplement and give baby food now. I think it's starting to decrease my supply because she never seems satisfied after just nursing now. pumping hasn't seemed to help. It seems like she likes the formula better than my milk. Should I just switch to only formula and baby food or is the little bit that she is getting worth continuing? If I keep nursing her will i keep producing some milk, even if it's just a little, or while I still dry up? I wanted to nurse for 2 years, but now a year doesn't even seem possible.