Was dumbledores sister a Obscurus?

Albus Dumbledore's Headmaster of Hogwarts School of Witchcraft and Wizardry had younger siblings called Ariana and Aberforth Dumbledore. Ariana stopped using or letting out her magic due to an incident with some muggle boys when she was 6 years old, this traumatised her from ever using her magic. It is understood that the boys saw Ariana using her magic through the bushes in the garden, the muggle boys attacked Ariana when she couldn't show them how to do the "trick". This attack eventually led to their father (Percival Dumbledore) revenging himself on the muggle boys concerned. This led to Percival's imprisonment in Azkaban for the crime, although it is not entirely clear what Percival Dumbledore did to the muggle boys. Aberforth asserts that Percival attacked the muggles whereas Muriel (Ronald Weasley’s aunt) suggests that he killed the boys.

Ariana's refusal to use her magic or to learn to control it and it being described by Aberforth as turning inward, driving her mad, making her dangerous and her powers "bursting" out of her. This leads me to believe Ariana became an obscurus (known as an obscurial).

An obscurus is created when a child denies their powers or suppresses them, this is usually due to a traumatic event such as in Ariana’s case or abuse and/or fear, an example of this is Credence Barebone (Aurelius Dumbledore?). Hatred towards their magical powers can make the powers turn inwards and become a dark, destructive and parasitic force on the person. This is why I think Ariana needed to be kept “calm and quiet” so she didn’t literally explode. This duty was something which Aberforth was keen to take over when his mother Kendra passed away.

Aberforth and Ariana bonded whilst feeding the goats together, hence all the references to Aberforth’s fondness towards goats and his Patronus being in the shape of a goat. A Patronus being something that comes from happy positive memories, I can see how losing Ariana could have destroyed Aberforth – all his happy memories are around feeding the goats with Ariana. Apart from Ariana being the guide into the Room of Requirement I think Aberforth kept a painting of her for sentimental reasons as well.

Also, I suspected that Ariana’s Obscurus is what killed Kendra Dumbledore as the outbursts of an obscurus tend to be focussed on the person tormenting the obscurial. Kendra Dumbledore is described by some as being a hard woman, domineering and concerned by what others thought. This may have stemmed from this incident and her desire to protect her family and keep them together no matter what meant having to conceal Ariana’s existence. Percival obviously went along with this as he never admitted why he attacked the muggle boys; this was in order to keep Ariana from being locked up in Saint Mungo's Hospital for Magical Maladies and Injuries for the rest of her life. Kendra's keeping quiet, having discipline, and calm may have been perceived by an outsider as Kendra being a strict and difficult lady to live with. Ariana essentially being kept prisoner at home (for everyone's safety) and only going out for walks in the garden at night would only add to people's perception of Kendra as a stern woman. Kendra being concerned by what people thought or even knew about her family would also be coming from a place of protecting her family but again this could be misunderstood as being stuck up, self-important etc. I cannot imagine this enforce prison that Ariana lived in made her feelings towards her captor and carer Kendra any warmer.

We can never be sure what happened between Kendra and Ariana for sure,other than it resulting in Kendra's death.

In Fantastic Beasts and Where to Find Them Newt Scamander explained that Obscurial's didn't live to be very old, one girl he came across in Africa dying at the tender age of 8. This is where Newt obtained an obscurus which he got from the young girl before she died. In Ariana’s case of obscurus/obscurial she may have been one of the oldest obscurial's at approximately 14 when she died. It is unknown how much longer Ariana would have survived as an obscurial; she died getting in the middle of a dual between Aberforth, Albus and Gellert Grindelwald. Sadly, both brothers blamed themselves for her death.

Credence Barbone is thought to be the only obscurial that lived longer, living into adulthood. Credence is believed to be a long-lost brother or relative of Albus, Ariana, and Aberforth; Credence's birth name is thought to have been Aurelius Dumbledore.

Family Tree https://time.com/5457412/fantastic-beasts-2-dumbledore-family-tree/