If I read the post correctly this calf is now only 5 weeks old.... NO.... do not decrease her milk. She would be getting the most milk from the cow about now... cows will come into the greatest amount of production after 30 days.... most dairy cattle peak at 45-125 days... Look at calves on cows... they get chubby fat after 6 to 8 weeks... because they are getting what they need and are putting on good body condition... They are growing.
I would not increase her milk as this limited amount is encouraging her to try and eat the feed you are providing. I would start to increase the amount of feed after a week of cleaning it up.... and I would stop sprinkling the milk replacer on it so she will get just the taste of the feed.
There are lots of thoughts on milk feeding/ bottles for calves. It used to be strictly a 2 qt bottle 2 x a day was plenty... There are alot of dairies that are now feeding 3 qts a feeding... and getting impressive growth of their heifers. If you have waste milk on the farm... treated or high cell count milk that a farmer will keep out of the tank... then 3 qts is fine. Buying milk replacer is expensive, 2 qts is adequate with the calf starting to eat. Some dairies have weaned calves at 6 weeks but it takes alot more feed to get them to continue to gain.... just not worth it if you want the calf to grow at a decent rate.
I feed bottles for 8-12 weeks... depending on the calf... 12 weeks is better... more like NATURE...but can be very expensive...
The "true milk stomach, section" will shrink as they eat more... but think about calves on beef cows... most are not weaned until 5-8 months... and they are still getting some milk all along. The better the cow milks, up to a point, where it will damage the udder because the calf cannot use all the milk..... the nicer/fatter the calf is and the better it grows...
Don't short change the calf now that it is starting to eat.... at 7-8 weeks, you can cut the milk back... and take 3-4 weeks to cut back more as you wean it off...