Trish Belloptrix is one of the many characters touring with Master Payne's Circus of Adventure. She's the one who welcomes ✣ Agatha Heterodyne to the Circus when she and Krosp show up with Trish's lost son Balthazar in tow. Apart from being a comfortably motherly figure, she actually doesn't have a huge role in subsequent events, with one small but important exception.
Trish apparently walks with the aid of a crutch, which is actually mildly remarkable given the number of low-grade Sparks in the Circus who'd love to "improve" ✣ injured legs (the second novelization states briefly that she has only one leg). However, the crutch may have a dual purpose: big nasty gun. At least she's wielding ✣ one during the fight with the Monster Horse Beastie, although the rounds it fires serve only to make the MHB mad, rather than render it into (monstrous) horse meat. It's not clear that the crutch actually turns into a gun, but nothing else about Trish gives the impression that she's packing heat.
She's married, as far as can be told, to Balthazar's dad, who doesn't get a name in the comic, but is called Guntar in the novelizations. Balthazar confides ✣ , in the scene with Smilin' Stev, that his mom likes 'em "big and slow and stupid." Since Mr. Belloptrix is at least big and slow (he frequently plays Punch in the Heterodyne shows), he's close enough to satisfactory that she probably doesn't care that much what his name is.
Her official duties with the Circus include applying ✣ the actors' makeup for Heterodyne shows.