На подготовку к встрече у неё ушли полторы недели, зато презентация вышла отличной.

Here уйти is being used in an idiomatic way. In the pattern уйти на + accusative, it means to be spent on, to go into, or to be used up by something.

So:

• На подготовку к встрече ушли полторы недели
  = A week and a half went into preparing for the meeting = It took a week and a half to prepare for the meeting

The perfective past ушли presents the time as a completed whole: that amount of time was fully consumed.

Russian often uses у + genitive to show the person whose time, energy, or resources were used up.

So:

• у неё ушли полторы недели

literally feels something like:

• from her, a week and a half went

but in natural English it means:

• it took her a week and a half

This construction is less direct than Она потратила полторы недели... and focuses more on the time consumed than on her deliberate action.

Compare:

• Она потратила полторы недели на подготовку = She spent a week and a half preparing
• У неё ушли полторы недели на подготовку = It took her a week and a half for the preparation

Both are correct, but the nuance is a little different.