Learn Hardcore Hebrew: הם רוצים להתחתן בקיץ, ולכן היא הייתה צריכה לבחור טבעת כבר החודש. - They want to get married in the summer, so she had to choose a ring already this month.

Breakdown of הם רוצים להתחתן בקיץ, ולכן היא הייתה צריכה לבחור טבעת כבר החודש.

Why does the sentence start with הם but later use היא?

Because the first clause talks about both of them:

הם רוצים להתחתן בקיץ = They want to get married in the summer

Then the second clause narrows in on the woman specifically:

ולכן היא הייתה צריכה לבחור טבעת כבר החודש = and therefore she had to choose a ring already this month

So the meaning is something like: both partners want to get married in summer, and because of that, she had to choose a ring this month.

What does להתחתן mean, and why does it start with לה־?

להתחתן means to get married.

The prefix לה־ is the normal infinitive marker in Hebrew, similar to to in English:

So after רוצים (want), Hebrew uses an infinitive:

Why is להתחתן used instead of a verb meaning to marry?