After my wife died I found that she existed in my mind quite a lot (as well as formerly existing physically).
That existence (in my mind) could make me happy ("what a privilege to know her") or sad ("miss her dearly").
Whether I'm sad or happy is partly my choice, it's not inherent in or obliged by the physics of the situation -- instead a matter of how I train myself (habitual thought), a.k.a. it depends on how I "view" it.
On the subject of memory, one of the things to remember (according to Buddhism) is "virtue" -- for example skilful, altruistic, compassionate behaviour -- "recollection of virtue" is an mind-object whose result or purpose could be an "absence of remorse". So when people behave virtuously, remembering that doesn't cause regret -- instead, looking back, "I'm glad she did that" and "I'm glad I did that" and so on.
Because it's a matter of doing the best you can in the circumstances.
So my question is this: what would Buddhism say that happened to my daughter? What is she today? Where is she? Is she still my daughter or has reincarnation taken place? What is the purpose of her being damned to this state?
If Buddhism were speaking carefully I think it would adapt what it says according to what you understand and know -- perhaps a gradual training.
I tend to think of Buddhist doctrine as starting with "the four noble truths", but according to this topic it might begin with talking about ethics, and generosity, and heaven.
Then there are the four noble truths, which are approximately (as I remember them):
- Birth, sickness, death, are dukkha (the word dukkha is translated variously as "suffering" or "stress" or "unsatisfactory"); and not getting what you want, being exposed to what you don't want, not being able to keep what you want to keep, are dukkha; in short, the five "aggregates of clinging" are unsatisfactory.
- Dukkha is associated with tanha (literally "thirst", usually translated "craving") craving for sense-objects, craving for becoming/existence, even the craving for ending
- Dukkha ceases when craving ceases
- There's a way (Buddhist practice) which leads towards the complete ending of craving and suffering
So apparently suffering arises with (and results from) various forms of craving -- wanting things to be other than as they are.
Another important part of the Buddhist doctrine is that everything that's put-together (including "beings") is impermanent -- so I guess you'd better not expect "compound things" to last forever ... including "human bodies" (but even also day-dreams may be fabricated and based on a false assumption that the body is under your control, e.g. that it remains healthy and unchanging).
Buddhism also praises "seeing things as they really are" -- which includes seeing, "they're impermanent" -- but I think that also includes seeing a distinction between moral and immoral (seeing kindness, altruism, and so on).
There's another doctrine, the anatta or "non-self" doctrine. If the four noble truths are the first doctrine then anatta is the second. It might be difficult to understand or explain -- those who do understand might be called semi-enlightened, there are dozens of questions about it on this site -- it might be summarised as "any view of self will result in dukkha" -- where examples of "self-view" include "I exist" but also "I don't exist" and "this is me" and "this is mine" and "this is my permanent self".
For that kind of reason the question "What is she?" is difficult to answer in a way that wouldn't cause you pain -- I think that Buddhism might say that there is no satisfactory answer to that question.
Going further the question might be described as the product of unwise attention. Conversely "wise attention" focuses on questions like "what is stressful?" and "what is not?" -- for example, "recollection of virtue" and questions like "what was virtuous?" and "what is virtuous now?" might be a more kind of "enlightening" way to try to think about things.