Why did Juilet kill herself if she had two other choices?

From the text, we can infer that Juliet chose to enter enternity with Romeo. No other reason is given for her decision.

What’s here? A cup, closed in my true love’s hand?
Poison, I see, hath been his timeless end.—
O churl, drunk all, and left no friendly drop
To help me after? I will kiss thy lips.
Haply some poison yet doth hang on them,
To make me die with a restorative.