We all know Jill Duggar is not very close to her family.

We know this because Jill Duggar has said it.

Following several months of either being quiet or simply being mysterious while her husband, Derick Dillard, hurled insult after insult at her dad... Jill at last came clean in October.

She outlined exactly why she's so estranged from her loved ones.

We thought, however, that Jill mostly had beef with just her mother and father.

She talked at length in an interview with People Magazine and then in subsequent YouTube videos that Jim Bob and Michelle greatly limited her opportunities outside of the family's TLC program, emphasizing that she felt too controlled by her parents.

Makes sense to us, based on what we know.

But does Jill also have an issue with her siblings? Specifically, with sister Jana Duggar?

We ask because twins Jana and John David turned 31 years old over the weekend.

To mark the occasion, Jill shared a throwback photo of herself and the pair (below) and wrote as a caption to the cute snapshot:

Throwback to many years ago (L to R: Jill, Jana, John). I laugh a little at this pic because, believe it or not, it displays our personalities at the time pretty well...

John and I just chilling and Jana all over the place!

Jana? All over the place?

The same Jana who, as an adult, seems very calm and quite cool and totally collected at all times?

Jill is the one who has proven herself to be rebellious of late -- while Jana has never said a cross word about her mom and/or dad and Jana is the one who seems very much content and stable under the direction of Jim Bob and Michelle.

In comments on Reddit, users are now wondering if all the spunk has been squashed out of Jana after years of living under Jim Bob and Michelle's thumb.

"I sometimes get the sense that part of the reason Jana never married is because she still has that streak of stronger personality," one person wrote.

"It's been pretty suppressed, but I feel like sometimes it comes out on the show.

"She loves planning events and isn't shy about telling everyone what to do.

"Maybe she was afraid of getting married because of that."

Indeed, Jana is 31 and single. Which is nothing short of unheard of for a Duggar woman.

A month aga, Jana said she misses being around her sister and added that she's praying for Jill and Derick's salvation.

A nice sentiment, to be sure.

But also a condescending one? Might Jill have taken some offense and might she have thrown a bit of shade here in Jana's direction as revenge?

Maybe.

But also, maybe not.

Might Jill also just be sending a message to Jana via these birthday wishes?

Might she be saying that it's fun and liberating to break free from the Duggars and that her sister -- who was once "all over the place" -- should go ahead and take a chance and join her?

Maybe.

But, again, maybe not.

It's hard to say at this point.

View Slideshow: Duggar Swimsuit Photos Revealed: How is That Comfortable?