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WENN / WireImage 1 / 6

By Kat Giantis

We readily admit we're not the biggest fan of LeAnn Rimes. Her seeming smugness over her twoo lurve with newly minted fiancée Eddie Cibrian makes us stabby, especially given that their relationship began with both of them two-timing their spouses.

And one of those spouses is still smarting.

This week, the actor's ex, Brandi Glanville, took to her Twitter to slam LeAnn for turning up at a school event for 7-year-old son Mason (Brandi is also mom to Eddie's other son, 3-year-old Jake).

Seems the increasingly hungry-looking singer plans to belt out a tune for the tyke's class, who, let's face it, would probably prefer a private performance from Justin Bieber.

"I told Eddie to please tell you that I think it is highly inappropriate for you to sing in my sons class on Friday," fumed Brandi. "Boundries!!"

Glanville believes LeAnn, who isn't yet the boys' official stepmom, should back off and let the parents take center stage.

"It's Mason's week [to] share his family with the class. it isn't ur place," she tweeted. "Let Eddie read a script. You are not his parent. RESPECT!"

We're not sure a bunch of little kids would enjoy the underemployed Cibrian reading selections from his fine work on "CSI: Miami," but we're certain of one thing: This discussion should not be taking place on Twitter.

And as much as it pains us to point it out, Rimes, who took her insanely active Twitter account private in January, has decided to detour onto the (slightly) high(er) road.

"Once again, if you retweet me drama I will block you," LeAnn warned on Thursday. "I don't want it on here period!! Let's stay positive and focused on the good :)"

RELATED VIDEO: Did LeAnn get a boob job -- from Brandi's plastic surgeon?

Still, when one of her followers wondered why some people start "tweet wars," because "they sure wouldn't say things to your face!" the future Mrs. Cibrian No. 2 responded, "exactly...well, some might and more."

LeAnn's social networking reserve is a new thing. Let's not forget that time she tweeted about taking Jake to the emergency room -- apparently before calling Brandi with the news.

"All I know is I didn't get a phone call," Glanville fumed to E! News at the time. "Poor choice. Bad parenting."

Eddie, LeAnn and Brandi have gone to counseling together for the sake of the kids, although it hasn't gone very well.

"There is still a lot of animosity, but hopefully, one day, we can move through that and get to a better place" said Glanville, who once accused Rimes of "Single White Female-ing" her ("She wants my life. She wants my kids. She wants my husband. She can have most of everything but just not my children or my family").

What do you think, people? Is LeAnn overstepping her future stepparent boundaries? Should all three work harder at their counseling sessions? Tell us in the comments.

Meanwhile, in still more Rimes news …

In Touch has branded her a Bridezilla, alleging that she's going overboard with her impending nuptials.

RELATED: Couples at the Grammys

"LeAnn selected three different gowns: one to walk down the aisle, one for the dinner and another to dance in," says a source, with another snitch adding that the bride has spent more than a month "perfecting her vows" and "is planning to serenade Eddie with a medley of songs."

As for Rimes' increasingly svelte figure, "She has been working out nonstop," maintains the spy. "The way she talks about the wedding, it's like she thinks she's Kate Middleton and Eddie is Prince William!"

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