Maybe all that growing and milk making is from her worrying about Sunburst so much.  
So much pressure She imagines her little teat squisher may going through now working with royalty and national security. Bet she wonders if he’s eating enough, no doubt her udders responded to that hypothetical problem subconsciously.
 
Know a mom like her has to wonder if Sunburst finally met a mare and if she’s nice, or some jezebel cow looking to take advantage of her baby boi. That thought alone should get her motherly instincts into full swing…meaning more growth.