Women typically feel fat and unattractive after giving birth. It’s hard work! I think that by showing herself so fit after three kids she’s actually trying to give them encouragement.
She could have phrased it a little differently, something like, “Hey, ladies, if I can do it, so can you! Take heart, you can get in shape after babies! C’mon, you can do it!” instead of “What’s your excuse?” That “What’s your excuse” may have rubbed people the wrong way. But I think she looks great and it’s nice to see an apparently happily married young lady with three adorable children and a positive attitude!