I am not sure this is really advise, as much as observations. Looks like your LO is getting plenty to eat, esp in the formula category. You are still doing 5 bottle feeds, and until this weekend, so were we. Perhaps that is the reason yours wants less of her DF? I still do a DF at 10:30 and I have absolutely no plans to drop this. Some nights, mine takes only 4 oz, other nights, she takes all 6. I have found that a lot of it has to do with where in her sleep cycle she happens to be when I feed her. If she is pretty much fast asleep, she takes the bottle really easily and drains it. If she is more alert, she does not seem as interested. Maybe you can slightly play around with the time you offer it and see if it makes any difference. Also, maybe you can space out the bottles during the day from 4 hours to 5 hours and thus drop one of the bottles. Instead of 7, 11, 3 and 7 you could try 7, 12, 5 and then just the DF. I only suggest that because at 8 months, 5 bottles is a bit much, and it seems like yours is getting plenty from the amounts you are offering. Plus, she might start to increase her appetite for solids (mine currently takes about 4 oz three times a day).
Not sure if these changes are going to help with the sleeping issues you are having, but I certainly wanted to say that from what you describe, I don't think I would describe her as "not a good eater", but I know exactly how you feel b/c DD1 was (and still is) really tiny.