In "Romeo and Juliet", how does Juliet feel about Tybalt’s death?
Juliet feels sorrow over Tybalt's death, but she's more relieved that Romeo is alive and grateful that Tybalt didn't kill him.
When Juliet finds out that Tybalt is dead, she discovers in the next breath that Romeo, her secret love, has been banished from Verona. She doesn't have time to process Tybalt's death separately from Romeo's banishment. She says:
That "banished." that one word "banished"
Hath slain ten thousand Tybalts. Tybalt's death
Was woe enough, if it had ended there.
Or, if sour woe delights in fellowship
And needly will be ranked with other griefs,
Why followed not, when she said "Tybalt’s dead,"
"Thy father" or "thy mother," nay, or both,
Which modern lamentations might have moved?
She means that the pain of Romeo being cast out is equal to ten thousand times the pain she felt at Tybalt's death. Juliet also says that saying Romeo is banished is like saying her parents, Tybalt, Romeo, and herself are all dead. So the pain of Tybalt dying is much eclipsed by the pain of losing Romeo. Later, she says that she'll still be crying for Romeo's banishment even when her family has stopped crying over Tybalt's death.
While Juliet is upset that Romeo killed her cousin, she justifies it to her nurse by saying that if he hadn't, Tybalt would have killed him. She says that her husband being alive is comforting news, even though it means the death of her cousin.
In Act III, scene II, Juliet is confused by the Nurse and her sobbing. At first she thinks that Romeo is dead. The Nurse does nothing to correct her at first. Then the Nurse says Tybalt's name. So because of all the confusion in this scene between the Nurse and Juliet, Juliet is not truly able to grieve properly for her cousin. She is upset that he's dead, but she has mixed emotions going back and forth about how she feels about Romeo. How could he do this?
"O serpent heart, hid with a flowering face!
Did ever dragon keep so fair a cave?
Beautiful tyrant! fiend angelical!
Dove-feather'd raven! wolvish-ravening lamb!
Despised substance of divinest show!
Just opposite to what thou justly seem'st,
A damned saint, an honourable villain!"
He appears angelic, yet he murdered her own blood. She's confused. So she is not able to fully grieve for Tybalt. She's more worried about how that affects Romeo and if they can still be together. She does use her so-called grief over Tybalt's death to avoid a lengthy conversation with Paris.
At first she is upset and angry because her husband killed her cousin, but after she realizes that if Romeo didn't kill Tybalt he would have killed Romeo. She then sides with Romeo to be loyal and after that we don't hear anything about her feelings for Tybalt. Most likely she doesn't care much after.
However, in Act 4 - Scene 5 when she is talking about being in the tomb with Tybalt's dead body she mentions at the end of her soliloquy how his ghost will try and get revenge on her. Maybe she feels guilty here?