Cadence was born a pegasus, then ascended (became an alicorn) when she was very young- about 15 or 16. Her magic was promising in Celestia’s eyes, and thus she was handpicked as Celestia’s heir. Cadence instead went on to rediscover a lost civilization, the Crystal Empire, which she ruled as its Queen for 25 peaceful, prosperous years.

She is a descendant of an ancient royal family, the one that used to rule the Empire, hence her powerful connection to it which otherwise can’t be explained. No one knows this, not even her, but it is forever written in her blood. So, yes, in my headcanon, this does mean she is related to Sombra- very distantly, he’d be her great great great (the “greats” go on for some time) uncle.

Her magical affinity is light, which manifests itself in a more concentrated form: love.

Since he married Cadence, Shining Armor takes the title “King consort.” Later, when she marries Chrysalis, Chrysalis too becomes the Queen consort.

Her love magic includes all types of love, including platonic, romantic, comfort (love between child and parent)- it’s not limited to just one.

Cadence is able to replace the Crystal Heart and function as it. Her daughter, Flurry Heart, is born with this same ability, hence Flurry’s connection to the kingdom and her subjects. Cadence’s second daughter, Love Letter, even in all her power, does not have a connection to the Crystal Heart.

She is not as close to her daughters as she wishes she was. Flurry Heart is more responsive to her, at least, but Love is like a stone wall. She feels like she’s failed both of them- neither of them are anything close to benevolent. Flurry grew up with a massive ego, and bullied those she believed were below her (which was pretty much everyone). Love Letter grew up passive and inexpressive- Cadence never knew what she was thinking, or if her daughter even felt love at all. She certainly never expressed it. She convinced herself that perhaps Love Letter just had a different way of showing she cared.

After Flurry Heart loses her horn, Cadence falls into an unbroken silence, and becomes even more stonewall-ish than Love Letter. She trusts Love and believes she’ll do what is right for the Empire, but her faith in her daughter quickly plummets. Regardless, the Crystal ponies adore Love… so her rule can’t be as bad as Cadence thinks, right?

Cadence is not aware that Love Letter dislikes her. It’s almost ironic, because Cadence puts so much faith and love and trust into her, when all the while Love is plotting behind her back.

Cadence’s magical abilities include entering the minds of any creature- pony, dragon, hippogriff, etc- although some individuals can prove to be more stubborn and “fight back.” This is the same type of magic Sombra had, although he notoriously abused it. Love Letter views this type of magic as tyrannical, invasive, unjust, and immoral. No pony should have access to another pony’s mind, no matter their intentions.