By reaching for a big dictionary, perhaps. Suif means tallow or suet, while here's how the Oxford Hachette dictionary covers boule
La femme, une de celles appelées galantes, était célèbre par son embonpoint précoce qui lui avait valu le surnom de Boule de Suif. Petite, ronde de partout, grasse à lard, avec des doigts bouffis, étranglés aux phalanges, pareils à des chapelets de courtes saucisses; avec une peau luisante et tendue, une gorge énorme qui saillait sous sa robe, elle restait cependant appétissante et courue, tant sa fraîcheur faisait plaisir à voir. Sa figure était une pomme rouge, un bouton de pivoine prêt à fleurir; et là-dedans s'ouvraient, en haut, deux yeux noirs magnifiques, ombragés de grands cils épais qui mettaient une ombre dedans; en bas, une bouche charmante, étroite, humide pour le baiser, meublée de quenottes luisantes et microscopiques.(Maupassant, Guy de (2011-03-30). Boule de Suif (French Edition) (Kindle Locations 175-180). . Kindle Edition.)
So, on the analogy of boule-de-neige, the simplest version would be tallowball, which seems misjudged. But it's what this translation from the Gutenberg project (which quite cannily decides to leave embonpoint as is) goes for:
The woman, who belonged to the courtesan class, was celebrated for an embonpoint unusual for her age, which had earned for her the sobriquet of "Boule de Suif" (Tallow Ball). Short and round, fat as a pig, with puffy fingers constricted at the joints, looking like rows of short sausages; with a shiny, tightly-stretched skin and an enormous bust filling out the bodice of her dress, she was yet attractive and much sought after, owing to her fresh and pleasing appearance. Her face was like a crimson apple, a peony-bud just bursting into bloom; she had two magnificent dark eyes, fringed with thick, heavy lashes, which cast a shadow into their depths; her mouth was small, ripe, kissable, and was furnished with the tiniest of white teeth.
I suppose the real problem with tallow ball is that it doesn't sound attractive, and partly that's because the plumpish figure doesn't these days have the same attraction that it used to. So I think any translation needs to put some extra attractiveness back in. The best I can do at that moment is to take the hint Maupassant gives, and go for apple dumpling. It sounds slightly dated, which is OK, but also suggests a guilty pleasure.
I don't know whether to criticise that translation for omitting Maupassant's assurance that her eyes are "en haut" while her mouth is "en bas" on her face. Any decent editor would have cut those phrases. But it's not a translator's job (these days) to improve a text.
Anyway, I read Boule de Suif after The Guardian featured him in their history of the short story. It's cleverer than I first thought. After Apple-Dumpling's capitulation, the narrator points out too clearly, I thought, the hypocrisy of her fellow-passengers, and I wanted to say Yes, we get it. But what goes unsaid at this stage is the parallel between her and the invaded France. It takes a while for that to make its presence felt, but when it does, you realise why there's so much about the German occupation early in the story, where both sides - collaboration and resistance - are mentioned. It's as if the narration itself is too ashamed to point out that occupied France was also willing to be fucked over. As always, a connection that you spot for yourself is always more effective.
(... and reading Boule de Suif led me to reread Measure for Measure. Possibly more on that to come ...)