Does your colleague follow a lot of mummy bloggers on social media, by any chance? It sounds like that may be her only impression of motherhood.
Also, is she American? Is she in a country where 52 weeks of mat leave would be impossible to comprehend because the mat leave she could access herself is maybe just 6 weeks of disability?
If my guess is more correct than not, a polite reminder to your colleague that most social media accounts are marketing vehicles. Soft advertising for products. Those women work with PR teams: either the client's or their own. Their glossy looking posts about being on mat leave with a baby, and maybe "hustling" like the "girl boss" they are, tend to be, in other words, "professional bullshit".
And if she is indeed American (I am too) in "does not compute" mode about 52 weeks ... a baby is still very high needs at age 1. A different arrangement of needs, but still very high. If the childminder, nanny, grandma, or daycare staff aren't meeting those needs, then it has to be the parent on leave from work.
Honestly, the only way I could envision starting my own business on mat leave would be if I'd been made redundant, needed income beyond SMP to survive, and had very few employment options available (because of recently having a baby). That's not the same as a 52-week period where your job is waiting for you by law.
"Starting your own business" can be limited to registering an LLC and doing nothing much more than that as well. Because hey, you've started.
Considering how many people actually starting their own businesses work crazy hours in the early years developing plans, getting finance in place, marketing, launching, and applying lessons learned to the original plans and financing structure.... I don't think many of us would do that with an infant unless we had to.