Elle had her hopes very high expecting Warner to propose, only to have her heart broken when Warner instead misleads her then breaks up with her. After that she spends a week locked up in her room. Even if it wound up being for the best at the end, it's pretty depressing to see.
Warner tells her that he needs someone serious, and Elle heartbrokenly responds "but I'm seriously in love with you".
"I'm never gonna be good enough for you, am I?" Though this is the beginning of Elle's transformation and confidence boost, it's a bit sad to see her finally realize that Warner never thought she was capable of doing anything besides being pretty.
For the same reason, Elle's reaction when Callahan tries to seduce her, which almost causes her to give up trying to be a lawyer.
"Oh, God... I feel terrible, I made a huge mistake."
A small one, but when Warner says "Forget about Brooke, look out for yourself." Vivan gets an extremely sad look on her face as her eyes drop.
Right before Elle gets the pep talk from Stromwell, she cries to Paulette that people only see her as "blonde hair and big boobs", calling herself a joke. Paulette likewise seems heartbroken as she tells Elle "you're not a joke", wishing her friend could see the intelligent, caring person she owes so much to.
While it's not touched on too much, despite the age difference, Brooke's marriage was one of genuine love, and she's lost the love of her life all because of an insecure stepdaughter. Her voice cracks as she insists to Callahan that "I loved my husband".
And while she's pretty awful, Chutney starts crying as she confesses that she didn't mean to shoot her father.
David getting turned down by those mean girls who call him a dork. He can only feebly reply that he's in law school. While the girl obviously had the right to turn him down, she and her friends are so mean.
The Musical
The titular song, "Legally Blonde". Elle giving up on her dreams almost before they've begun, and Emmett begging her to stay... her resignation is heartbreaking, and his desperation just makes it all the worse.
Emmett: What about love? I never mentioned love - the timing's bad, I know. But perhaps, if I'd made it more clear that you belong right here, you wouldn't have to go, 'cause you'd know that I'm so much in love...
Elle: Back to the sun, back to the shore, back to what I was before...
Emmett: Please will you open the door?
Elle: Lie on the beach, dream within reach, don't stray beyond...
Emmett: We both know you're worth so much more!
Elle: Some girls fight hard, some face the trial, some girls were just meant to smile... that's fine with me, just let me be "Legally Blonde"...
Emmett: If you can hear, can I just say - how much I want you to stay?
Elle: It's not up to me, just let me be "Legally Blonde"...
Emmett: I need you to stay...
Elle: It's not up to me! Just let me be "Legally Blonde"...
Just the way her voice breaks on the word "smile."
Emmett's plea for Elle to stay: "What about love? I never mentioned love. The timing's bad, I know..."
"Ireland" is pretty sad too, when you consider the fact that Paulette doesn't have the same kind of faith in her own happy ending as she does in Elle's. Good thing they both get theirs at the end.
In the MTV airing, at least, Brooke's expression when she learns that her stepdaughter wanted to kill her. In the film, she just grins in smug satisfaction that she's not going to jail, but in this performance, she seems genuinely hurt and nearly faints, only for Carlos and Nikos to catch her just in time.
