- Crossover episode Jossed at least.
It's possible to interpret the various continuities of Jewelpet as representative of different time-periods of this hypothetical universe (assuming that only the TV series are canon):
- Kira Deco would be the earliest to occur; humans are very unusual and something of an anomaly in Jewel Land. Additionally, they cannot travel between Earth and Jewel Land as they please, which implies that magic hasn't reached the level of the other seasons.
- Twinkle would happen next; now, selected humans are able to travel between Earth and Jewel Land with the express goal of learning magic. However, Jewel Land still refuses to reveal itself fully to humans.
- First series comes next; here, Earth and Jewel Land become fully aware of each other and decide to cooperate towards aa better future for both worlds. There's also mention of a past where humans and Jewelpets used to live in harmony, before Dian's rebellion made them distrustful of each other and caused them to keep to their own worlds, with Earth eventually forgetting about Jewel Land altogether, but NOT vice-versa. This past could take place between Kira Deco and Twinkle, or after Twinkle altogether.
- Sunshine and Happiness happen a long while after the first series, and likely at the same time, due to the similar settings. Humans and Jewelpets now live side-by-side, attend the same schools, and even have the same jobs. Travelling between the worlds is easy and habitual.
- Magical Change shows the disbelief in magic alluded to in Sunshine reaching critical mass, with a castle from Jewel Land falling in the human world because the disbelief is causing Jewel Land to rot. Jewelina may have stopped existing because of this situation, which is why she now has to be elected and ascended from a Jewelpet.
- Lady happens last. Let's say that the Lady Jewel position is an evolution of the Jewelina election from MC, which has become institutionalized through the Lady system. Dark Magic also seems to have evolved judging from the Beasts and the Door to Chaos; maybe they are a consequence of Jewel Land's rotting in MC. The human population seems to be far larger now; Momona and co. are Jewel Land-born humans.
- Maybe the failed regeneration of the Majos is a consequence of quashing Dian's rebellion. Jewelina became fatigued against the formidable opponent and split into four as a result. The newly incarnated Majos were at full strength and managed to finally defeat Dian. But the wonky regeneration leaves each Majo at only one fourth of the usual power and vulnerable to the effects of a lunar eclipse, which is why they need to collect graces every time one happens.
Io and Macaronia are her parents, because why not (if it makes you more comfortable, refer to the "pets are not unique" part of the shared universe WMG).