Learn Hardcore Japanese: kaimono no toki, kanozyo ha oturi wo morai wasureta. - While shopping, she forgot to get her change.

With nouns, you attach の to link them to 時(とき): N + の + とき = “when/at the time of N.” So 買い物のとき = “when shopping/at the time of shopping.” You can’t say 買い物とき.

Could I say 買い物する時 instead of 買い物の時? Any nuance difference?

Yes. Both are natural.

買い物の時: a broad “on the occasion of shopping,” covering the general time period of a shopping trip.
買い物(を)する時 / 買い物している時: highlights the action of doing the shopping (often felt a bit more “during the act”).

What does もらい忘れた literally mean, and how is it formed?

It’s “forgot to receive.” It’s the pattern V‑ます-stem + 忘れる = “forget to V.”

もらう → もらい + 忘れる → もらい忘れた (past). A more explicit alternative is お釣りをもらうのを忘れた. Synonyms: 受け取り忘れた, 取り忘れた.

Why is お釣り marked with を?

Because it’s the direct object of the intended action もらう (to receive). The underlying structure is “(She) receives change,” i.e., 彼女は（店員から）お釣りをもらう. Here it’s “forgot to receive,” so the object stays お釣りを.

From whom is it received? How would I say that?

Add the source with から (or に):

彼女は店員からお釣りをもらい忘れた。 Both から and に are used with もらう; から clearly marks the source/donor and is very common.

Why is there an お before 釣り?

It’s the polite/beautifying prefix お. お釣り is the standard polite way to say “change (money returned).” Without お, 釣り can sound clipped or technical; with お, it’s the everyday form you’ll hear.

Does 釣り also mean “fishing”? Is that confusing?

Yes, 釣り commonly means “fishing.” In money contexts people say お釣り, which prevents confusion.

Is お釣りを忘れた acceptable?

It’s unnatural for “forgot to receive the change.” 忘れる by itself usually means you forgot the thing in memory or left it behind unintentionally. For this situation, say:

お釣りをもらい忘れた / 受け取り忘れた / 取り忘れた.

Why not もらって忘れた?

もらって忘れた means “received it and then forgot (about it),” which is different. もらい忘れた means “forgot to receive (didn’t receive it at all).”

Can I omit 彼女? Do Japanese normally say “she”?

Yes, if the subject is clear from context, you’d usually omit it:

買い物のとき、お釣りをもらい忘れた。 (“I forgot my change (to receive it).”) Also note 彼女 can mean “girlfriend” in many contexts; as a standalone subject pronoun, it’s used but less often than in English.

Why is it 彼女は and not 彼女が?

彼女は: sets “she” as the topic (what we’re talking about) and sounds neutral.
彼女が: marks “she” as the focused subject, often contrasting with someone else (it was she who forgot). Both are grammatical; choose based on focus.

Could I say 買い物のときは instead of 買い物のとき?

Yes. 〜ときは topicalizes the time and can add a slight contrastive feel (“when it’s shopping time, (as for that,) …”). Without は, it’s a simple time adverbial.

What’s the difference between とき and ところ?

とき = time/occasion (broad).
ところ = a specific stage of an action (about to do / in the middle of / just after). E.g., 買い物しているところ = “right while shopping,” more pinpointed than 買い物のとき.

Does this sentence mean the clerk shortchanged her?

No. It says she forgot to receive her change. If the clerk failed to hand it over, you’d say:

店員が渡し忘れた。 (The clerk forgot to give it.) If the amount was wrong: お釣りが足りなかった or お釣りを間違えられた.

Are there more formal or alternative ways to phrase this?

会計のとき、彼女はお釣りを受け取り忘れた。 (more formal/business-like)
買い物中に、彼女はお釣りを受け取り忘れた。 (“during shopping” nuance)
Polite past: もらい忘れました。

Should I write 貰い忘れた with the kanji for もらう?

It’s common and perfectly fine to write もらう in kana. 貰う exists but is less frequent in modern writing; many style guides prefer kana for everyday verbs like もらう.

What about spaces in the Japanese sentence?

Native Japanese writing doesn’t normally use spaces between words. They’re often added in learning materials to help segmentation. A natural version is: 買い物のとき、彼女はお釣りをもらい忘れた。

Any tip about tense with 〜とき?

With verbs, the form before とき shows relative timing:

出かけるとき = when (I’m about to) go out.
出かけたとき = when (after) I went out. Here we have a noun (買い物), so we use Nのとき. If you need a clearer “after” feel with shopping, use a verb phrase: 買い物をしたとき.