She does appear to be actually lactating, if you look at her nipples (and read the article), but I’ve heard of limited cases of that being triggered *just* by suckling and the accompanying behaviours. Apparently in some animals it’s enough to trigger lactation hormones.
We’ve got a long-spayed calico who comfort-nurses a year and a half old “kitten” she’s decided is her son. Silly big lummox...at least she isn’t lactating, that we know of, but it makes em both happy sooo.....
It’s not just animals. Humans can induce lactation the same way, and often do in the case of adoption, for instance. Google “adoptive breastfeeding”.
I don’t think you even need to “lactate” to look like that. I think the frequent sucking will cause those niples to swell a bit in reaction.