About Dakini and Dakas.

A Dakini, the kind in human form, is roughly equivalent to the Muse of Western stories. She inspires the male, taking him to the full expression of himself in the world.
The student has obstacles to the expression of his Highest Self. Releasing these pretty much always involves revisiting the trauma that originally set the resistance in place. This is catharsis, the intense and complete experiencing of emotion that has long been contained, resisted, bottled up.
This is why many stories of Muses and other forms of Dakini picture them as willful, capricious, massively egoic, vengeful … in a word: trouble. They use the full range of manipulative tools and shock tactics that wives and other women have. Deliberately.
An in-school joke: What's the difference between the Goddess and a Dakini?
Answer: You can negotiate with the Goddess.
From more modern times, legend has it that once upon a time, Timothy Leary met Crazy Charlie and had just one conversation with him. It went like this:

Tim to Charlie: WHY?

Charlie to Tim: Because the women have all the power.

There is a lotof truth contained in that brief conversation.
A Dakini is a woman. Women are powerful trouble. Sorry female beloveds, but this really is true from the male perspective. The male beloveds know what I mean. So what's the difference between anywoman = trouble and Dakinis = trouble?

The difference is awareness.

Most women use their power, unconsciously, with unconscious motivation and objectives. The manifestations of her power, the effect it has in the world around her is sometimes noticed, but remains mysterious to her. She likely has a nagging feeling that she's missing something, and is often a good source of income for cold-readers, fortune tellers, psychics and psychologists. They have a deep usually completely unconscious fear of anything in life not fitting how TV tells them things "should be". Collectively their power is immense, even though, individually, privately, they may have disagreements with the cultural way, they accept it's how things are done.
Somewhat more aware are women who use their power unconsciously, with unconscious motivation but for conscious objectives These are the women-warriors. Attila the Hens. Maggie Thatcher, St. Jean d' arc,Boudica, Poolan Devi Condoleeza Rice and less obviously Jane Fonda and Oprah. They have a cause, a battle to fight, and they often do so magnificently. They feel compelled, driven to their battles but are not in touch with the source of their motivation or aware of their real enemy. With just this degree of awareness, however, some of them really manage to rock the world!
More aware still are the modern Hetaeras who use their power still unconsciously, but with conscious motivation for conscious objectives. Women who don't accept cultural restrictions. They either cover up carefully like Glen Close in Dangerous Liaisons (at amazon or kalahari), circumventing the strictures of the Women's Union, or ignoring the hatred of their less evolved sisters, they pay the cultural taboos less than lip service.  They often have influence in the arts and politics. Lola Montez, Lilly St. Cyr, Marilyn Monroe, Madonna. Appreciated, even worshipped (often in secrecy) by men as the closest representatives of the Goddess they know.
Spiritually evolved, and greatly aware, a Dakini has one purpose – your spiritual advancement, from wherever you are to wherever you can go. She is operating consciously with Love and all the leverage that affords her, to pry apart defences, smash ego and put Truth where it can't be ignored – that you might wake up to your purpose, your flowering. She's an emissary of Life, tempting you to really Living, to experiencing the real fruits of your existence.
A Dakini can be loved, adored, worshipped… that's essential… but she can never be owned. No artist, no poet could expect his Muse to be permanently available, or in any way exclusive, to him. They do what they do, live as they live so that they may serve existence in this way. Any restriction on their freedom, their flowering, is a restriction on their usefulness to existence. Another way to express this is to say that they are already married – to The Divine.
Dakas in this school, in sessions, work strictly to the directions of a Dakini when a female student (or another Dakini, or prospective Dakini) of theirs can benefit from something that particular Daka is practiced in. Very sensitive work indeed, and not often required. No, we're not hiring, please, guys, we're not even reading your applications anymore. Stoppit!
Dakinis and Dakas are those who know, at their deepest level, that this is their calling, their vocation. The commitment required is not "great" or "huge", it's total. Every aspect of being is involved. To work effectively with Tantra, an impeccable mind, a healthy body, an open heart and a significant degree of spiritual awareness are required.
So, for Dakinis, diet, exercise, meditation and some form of energy work are important. Dakinis work on themselves, their bodies and minds using Yoga, Tai-Chi, and practicing various arts along with lots of silent sitting meditation.
The Buddha's injunction to practice "right livelihood" is also important. Being involved in a business that profits from or causes damage to the earth is not compatible with tantric practice. Neither is being involved with any enterprise that derogates the Goddess, or any aspect of the Divine Feminine. These are not "rules", they are simply facts. Keeping the heart open and loving is essential to working with sacred sexuality. The heart can't be open when you're doing that which offends it.
The judgments of the surrounding culture also have to be faced. Many people focus on the sexual aspects of the work and reckon that "Dakini" is synonymous with "whore". Mainstream religions have done an effective job of convincing people that sex is inherently sinful, and this judgment has infected even non-semitic religions.
So a Tantrika, Dakini or Daka, has to face the same cultural judgment as a sex worker. She has to make a living from her teaching work, or supplement it with something compatible with her ethics/aesthetics. Maintaining her body, mind and spirit is a full time job, whether she has one client a month, or a dozen. Her lovers (outside of her healing work) are limited to those who have transcended jealousy, or willingly take on that journey. It really is a miracle that there are people in the world that are willing and able to do this work. It's not surprising that they are rare. Appreciate them.