Why has Beth never asked about her stuffs that Rio has stolen ? She’s much less materialistic than season 1 but after Boomer she could have negotiated at least for some, no ? Could it be guilt ? Or she’s just numb to everything and it’s a symptom of her depression ?
I'm actually not sure I would describe Beth as materialistic in the traditional sense. In season 1, she has a nice home and clothing and puts care into her appearance, but I've never gotten the sense that she cares to flaunt her wealth or is driven by having the best or nicest things.
I say this because I think Beth's drive to save her house isn't informed by the material aspects of it (it's size or neighborhood, it's acting as a symbol of her class) but by it's connotations of safety, security, and comfort. On top of that, it's not a definitive resistance to downsizing that has her fighting so hard to maintain it: it's that Dean has taken out three mortgages, meaning that even if they sold the house, they'd walk away with nothing. The house is one of the few things they have left with the position Dean has put them in.
In addition to that, they've shown that she's even somewhat economical. She'd scrimped on "pampering" herself (as indicated in the gap in her bikini waxes), defends Dean getting her coupons as a gift, regularly shops at a grocery store called Fine & Frugal, and we have seen her spoil herself only a few times—the first being when she bought herself a relatively understated necklace and the second when she, Ruby, and Annie went out on the town in a View from the Top. Even in that monologue, Beth's plan was for them to get into manageable financial situations and to have a honey pot for stability, not luxury.
However, I think there's a few reasons Beth has not asked Rio about her things. Beth asks Rio for favors that she intends to pay back or that she genuinely thinks are fair, but her responses to Rio's punishments are typically to get even/fight back or accept the consequences in some way, shape, or form.
She gets even or fights back when:
She gets Rio arrested after he sets her up with a test and fires her and she believes he's going to kill her
She steals the pills to wrestle 50% of the business from him
She breaks into his home to try and steal back the body, which she eventually finds
She draws a line in the sand and refuses to let Rio and Mick handle Max
She steals money from Rio in order to pay her bills after Rio murders Lucy and she realizes what they have is not a life
She tries to organize a hit on Rio when she believes that she's trapped in this cycle with him forever and doubles down on it when he gets her fingerprints on the gun
She presents his fingerprints on the money to him as retaliation for her fingerprints on the gun
She works with the Secret Service after he refuses to loan her money to get Dean out on bail for taking the fall for her
She turns him over to the Secret Service after he threatens to murder her family
She accepts the consequences when:
She gives Rio her own name in lieu of Mary Pat's after money goes missing
Rio shoots Dean to punish her for getting him arrested
She accepts the assignment to murder Boomer and learns to shoot after he catches her in the lie and says she's responsible for Boomer talking to the police
Rio charges her $200K to get rid of a body that he made her handle
Rio tries to run her ragged in 2.07, figuring out a way to do it all
Rio ropes her back into crime for Annie and Ruby's mistakes
She turns herself into the police when Rio refuses to help her deal with the Boomer problem
She settles for working for free in exchange for her life after the shooting
She figures out a way to get back up and running when Lucy's murder makes it harder for her to access the press after Rio kills Lucy to punish Beth
She delivers Boomer in order to get back on payroll
She does everything in her power to get Boland Bubbles in her possession when Rio refuses to pay her because he wants to know where her money is going
She may ask Rio for help often, but it is not something she enjoys doing. He really is her last resort and I think it makes her feel weak to have to go to him, doubly so when he ultimately refuses to help.
So I think in some ways, it's a matter of pride. She accepts the consequences as she's often done when she sees no other alternative, which really does show that despite all the ways that Beth has betrayed him, she feels that he has power over her. Really, the only power Beth has over Rio most of the time is the power he's given her because he is unable to pull the trigger because of his feelings for her.
On top of that, I'm not sure Beth believes that Rio still has her furniture because that would mean that she believes he saved it because he always intended to give it back.
As for trying to negotiate for it in the Boomer exchange, her main priority was getting back on payroll so she could fulfill the payment for the hit. Her top priority was getting control over her life back, and I think she felt that she could suffer without furniture for longer than she could suffer under the cycles of Rio's control.