My thoughts on which witches Shiroma is friends with - part 1
Let's start with something more obvious.
A doodle featuring Tuchikure, Madhata, GriRea, Sibuna, and Daimonji has appeared relatively recently. However, in this case, it's Tuchikure that's worth paying attention to: she directly addresses Shiroma while buying some "delicious sweets." The friendliness emanating from the the witch of the wasteland is clearly visible. And since the snow witch is in her company, it's quite possible she trusts her and her intentions.
My thoughts can also be confirmed by a more outdated DSP's work, which depicts Shiroma with a snowman and Tuchikure (foreground), as well as the Great Witch (background). The emphasis on Tuchikure and Shiroma can probably be interpreted as meaning they have a closer and more meaningful bond (for both of them, at least) than with the Great Witch (despite her being the most senior of the witches and clearly older than the snow witch and the witch of the wasteland). I also suspect that Shiroma and Tuchikure stand out in some way from the other witches in the Great Witch's entourage, as at the time of writing this post, the Great Witch has only appeared with 4 witches: Wadanohara, Chlomaki, Tuchikure, and Shiroma (Syokamori is her assistant, but hasn't made an official appearance together with the Great Witch in any DSP's works yet). I can't say for sure why DSP depicted them together in the same artwork like this. Perhaps they will have some kind of separate storyline in the future (like Wadanohara, Chlomaki, and the Great Witch, centered around Wadda's amnesia), but that's not certain…
Another small detail that hints at their friendship is the fact that Tuchikure "does not mind snow", despite "she lives in an arid place" where snowfall is clearly not a natural part of the weather conditions where Tuchikure lives.
Does this mean we could theoretically see Tuchikure visiting snowy places in the future DSP's works, where a Shiroma lives? Maybe.