Learn Hardcore Japanese: asita, kanozyo ha youzi de mukou no mati ni ikimasu. - Tomorrow she will go to the town over there for an errand.

は marks the topic: “as for her…”
が marks the grammatical subject and often presents/contrasts new or exclusive information.
With は, this sounds like neutral backgrounded info about her plan. With 彼女が, it would stress “it is she (not someone else) who will go.”
Note: the particle は is pronounced “wa,” not “ha.”

What does で mean in 用事で?

で after a noun can mark reason/occasion: “because of/on account of/for (some business).”
Natural alternatives:
- 用事があって… (since she has something to do…)
- 用事のために… (for the sake of some business; a bit formal)
Examples of this use of で: 事故で遅れた (was late due to an accident), 出張で東京へ行く (go to Tokyo on a business trip).

Can I say 用事に行きます to mean “go for an errand”?

Generally no; 用事に行く is uncommon/unnatural.
Use 用事で行く or 用事があって行く.
The pattern “V-stem + に” is for purpose with activities: 買い物に行く, 勉強しに行く.

What does 向こうの町 mean exactly—“that town” or “the other town”?

向こうの町 = “the town over there/on the other side (from here or from a reference point).”
It’s relative and a bit vague without context.
More specific options:
- 隣町 = the neighboring town
- あの町 = that specific town (both know which)
- あちらの町 = politer “that town (over there)”

What does の do in 向こうの町?

の links a modifier to a noun. Here it turns 向こう (“over there”) into an attributive modifier of 町 (“town”): “the town over there.”
Same pattern as 日本の会社 (a Japanese company), 駅の近く (near the station).

Why is に used with 行きます? How is it different from へ or まで?

に marks the destination/arrival point. It’s the most common choice in conversation.
へ marks direction; also correct here, slightly more directional or literary in feel: 向こうの町へ行きます.
まで means “as far as/up to”: 向こうの町まで行きます. You can also combine: 向こうの町まで行きます.

How can the non-past 行きます refer to the future?

Japanese “non-past” covers both present and future. The time word 明日 supplies the future sense.
To be more explicit about plans/intent:
- 行く予定です (it’s scheduled)
- 行くつもりです (I intend to)
- 行くことになっています (it’s been decided/arranged)

Can I rearrange the words or drop 彼女?

Does 彼女 mean “she” or “girlfriend”? How do I avoid confusion?

彼女 can mean either. Context decides.
To avoid ambiguity, use the person’s name + さん, あの人/あの方 (that person), or omit the subject.
Note: 彼女さん is used to politely refer to someone else’s girlfriend; don’t use it as a generic pronoun for “she.”

Do I need に after 明日? Is 明日に okay?

For relative time words like 今日, 明日, 来週, に is usually omitted: 明日行きます is natural.
明日に can appear when choosing/setting a time: 明日にします (“Let’s make it tomorrow”), but 明日に行きます sounds stiff/odd in ordinary speech.
Readings: 明日 is commonly あした; あす is a bit formal; みょうにち is very formal/written.

What exactly does 用事 cover?

用事 is a vague catch-all for “errands/affairs/things to take care of,” often without specifying details.
Common collocations: ちょっと用事があって…, 急用 (urgent matter), 私用 (private matter).

Are the spaces in the sentence normal in Japanese?

No. Standard Japanese doesn’t use spaces between words. The natural writing is:
- 明日、彼女は用事で向こうの町に行きます。
The comma after 明日 is optional but common.

Should it be 町 or 街, and how do I read 町?

Use 町 (まち) here (a town/municipality).
街 often refers to urban “streets/downtown” atmosphere.
In place names, 町 might be read ちょう or まち depending on the specific name, but as a common noun it’s まち.

Why not use を with 行きます?

行く is intransitive and doesn’t take a direct object; destinations are marked with に/へ.
を can mark the path/space you pass through: 橋を渡る (cross a bridge), 公園を通って行きます (go via the park). The destination itself still takes に/へ.