I had trouble saddling her too. You can watch her blow out like a ballon. I still check but I use holes for a marker. Ex: with Okie 6 showing. With her it's been 4. I wormed her last week because shes bigger than Okie. Anyway I started with 2 and waited awhile and walked her out and pulled to 3. Before I got on I put it on 4. She kept turning her head back like I don't know what she would have liked to do to me so I dropped it back down to 3. It still felt tight and no slipping noted. Don't know why she's getting bigger. I hope she's not expecting.
The difference in those holes is not much more than an inch, and they change from day to day, like we do. I would go by feel and not by what you think it should be counting holes. I thought you were treating her as underweight and feeding her up?
"Don't know why she's getting bigger."
You are feeding her better plus she may be happy that you own her now.