Linda tells her sons to leave because she wants to defend her husband from the emotional harm she sees looming in a another confrontation with Biff. She wants to save Willy from self-destruction and to keep her sons from leading Willy in that direction.

Willy is not in a good state of mind. He is in a poor state of mental health and Linda sees this clearly. She has found the rubber hose in the basement and she knows how fragile Willy is, mentally and emotionally. 

She feels that Biff and Happy are not helping Willy to recover. They are instead aggravating his condition, making him more nervous, more violent in his temper. They are moving him toward the edge. 

Biff and Hap’s insensitive behavior, she fears, will push Willy closer to despair and suicide.

While she worries that Willy might be pushed to take his own life, Biff and Happy do not know how to treat their father. Their behavior strikes Linda as completely uncaring. Her concern is spiked when they return from the restaurant where they were to meet Willy to celebrate the loan that Biff did not receive. 

...Biff and Hap enter late at night, finding Linda outraged at them for abandoning Willy at the restaurant.

At the heart of Willy's weakness is a profound self-doubt. Willy worries that he is a failure. Linda recognizes this. She sees also that Biff seems to want to tear down his father. 

Linda violently asks Biff whether he cares if Willy lives or dies.

Willy needs help, not an emotional challenge from his favorite son. Happy does not help either. He matches Willy's weakness with his own need for attention, further diminishing Linda's energies, which are required to make a last effort to save her husband.

When Biff and Happy return home after having abandoned Willy at the restaurant, Linda is waiting for them, angry almost beyond words at what they've done. She refuses to give up on Willy as her sons have apparently done; furthermore, she persists in her efforts to support and protect her husband. Because she knows about his suicidal thoughts and intentions, she worries about what may push him over the edge. Throughout the play, Linda is the character who consistently enables Willy by soothing his frustration and anger, accepting his "mistakes," for instance, about how much commission he's made, and attempting to find excuses for his often strange behavior. She dearly loves Willy, and if forced to make a choice between her husband and her sons, she will choose Willy.

Now that her sons have cruelly left Willy at the restaurant where they were all supposed to have had dinner--and abandoned him so that they could be with some women--Linda is disgusted with Biff and Happy. She apparently has never learned of Willy's affair with "The Woman," and she willingly accepts him with all of his flaws. That he's clearly falling apart mentally is a point she attributes to his being tired, probably because the future otherwise frightens her. Her sons are unreliable bums, as she points out, and they lack even common courtesy. If they don't love Willy, then they don't love her. She doesn't want them in her house.

Walking out the door with whores in tow, Biff and Happy leave their father to founder in his delusions in the restroom of Frank's Chop House. As they return home later that evening, Happy carrying a conciliating bouquet, Linda confronts her sons over humiliating Willy. Furiously dashing the roses to the floor, Linda castigates them as nothing more than animals and tells them to "get out of here, both of you, and don't come back!" In this pivotal event Linda demonstrates her intriguing character development. Through the course of the play, Linda travels a long way from the timorous housewife, almost mindlessly echoing Willy's fantasies, to a strong, fearless woman willing to stand up to her feckless sons. When the Loman family was younger, Linda was content to support and nurture Willy, but now that he cannot lead it out of its disintegration, she assumes that authority. In essence, she masculinizes her maternal role. But even with this movement, she refuses to sabotage his dignity. Thus, even though Linda knows that he is suicidal, she refuses to confront him.   

At the end of Act Two, Linda is disgusted that her sons had made off with a prostitute in a restaurant while Willy was in the "men's room" (toilet). In the heat of her anger she wishes them "good riddance," but in the end her maternal love brings her around. The family reconciliation is short-lived, however, since hard on the heels of this event is Willy's "accident," which all of them know is really a suicide.

Extra note:  The Loman sons' philandering is also a sour resonance of Willy's own infidelity and double-faced nature.  While his wife Linda trods around in mended stockings, Willy is offering expensive presents to his "conquests"  -- which besides being a betrayal in itself,  puts an extra strain on the family budget. Linda, who has been fiercely defending her husband up to this point, becomes increasingly aware that more than just one thing has gone awry within the family matrix.

Although she doesn't know it absolutely, it is already too late to save Willy, but she tries:

LINDA: Get out of here, both of you, and don’t come back! I don’t want you tormenting him any more. Go on now, get your things together!

Oblivious to Willy's deep suffering, Biff and Happy earlier abandoned their father at Frank's Chop house where they were all having dinner together:

LINDA: You’re a pair of animals! Not one, not another living soul would have had the cruelty to walk out on the man in a restaurant!

BIFF (not looking at her): Is that what he said?

LINDA: He didn’t have to say anything. He was so humiliated he nearly limped when he came in.

HAPPY: But, Mom, he had a great time with us...

BIFF (cutting him off violently): Shut up!

(Without another word, Happy goes upstairs.)

LINDA: You! You didn’t even go in to see if he was all right!

BIFF (still on the floor in front of Linda, the flowers in his hand; with self-loathing): No. Didn’t. Didn’t do a damned thing. How do you like that, heh? Left him babbling in a toilet.

LINDA: You louse. You...

BIFF: Now you hit it on the nose! (He gets up, throws the flowers in the wastebasket.) The scum of the earth, and you’re looking at him!

LINDA: Get out of here.

What Linda doesn't know is that without his sons, especially Biff, Willy has nothing. And with his sons, especially Biff, Willy has to face the lies that make up his life. So Willy just can't go on. There is no solution; she can't kick Biff out, and there's no way he can stay. Her husband is hopelessly doomed.