Hi and welcome to BW forums
Tbh at this age, do what fits best with your family and what you're most comfortable with. Personally, I liked to fix the start of the day to within half an hour of our preferred WU time, so if you'd like to keep WU around 7am, you could accept any WU after 6:30am as the start of the day, but wake her by 7:30am at the latest if she's still asleep then. So for example if she wakes at 6am for a feed and drops off again by 6:30 then I'd let her sleep until 7:30am, if she stays asleep that long, and shift the rest of the day accordingly. I'd probably also make up less formula for a 6am feed (I used to bf from one side only for this sort of thing) and then give her the rest at 7:30am. Does that sound like a plan?
Of course, if you don't mind getting up at different times every day you don't absolutely have to fix the WU, but I think many of us do find it beneficial to keep within a set range. Hope that helps?