Families are so interesting! I can't imagine sharing my FitDay with my Mom (if she were still alive) so she could check up on what I'm eating. You're an adult--you don't need her approval.
I think it's fine to celebrate milestones, but if I were in your place, I'd start drawing some boundary lines. Deflect the discussion by saying, "I don't want to talk about my weight now. Let's talk about something else." It will be awkward at first if she is pushy and used to being able to find out anything she wants by asking, but it doesn't sound right to me. Tell her you'll let her know when you reach your next milestone, and other than that, you'd just as soon discuss other topics. And stick to it!
Jay