When you are able to nurse her, does she get enough? Is this really an issue of low supply, or of simply not being able to pump enough? If she's getting enough from you, then don't supplement on those days. Only do it when you absolutely have to! Once you get to a year, if you still want to nurse her, she will probably be OK with just nursing when you're together. I worked for a while when my youngest was around a year old, & I was only ever able to pump enough for her to have one bottle of EBM when I was at work (that was her bedtime drink), and she nursed as much as she could when I wasn't at work, and cow milk & solids made up for the milk she wasn't getting. You're only four months away from the one year mark, so you're doing great, and I'll bet if you have to supplement it will only be short term.
(By the way, my youngest is still nursing at over three years old.)
Sabra: Mama to Bobbie (3/02), Linda (1/04), Esther (10/05), Marie (11/10), Douglas (11/12), & Psalm (09/14; in Heaven)