A: There are at least four ways to reconcile these accounts. Since Luke sums up what Mark says, I'm going to focus here on the difference between Matthew and Mark, in the interest of brevity.
First solution: Marks account about Jairus daughter and Saint Veronica (a traditional identification of the woman who had the issue of blood) is considerably longer. Matthew has abbreviated Marks material by removing entirely the messengers who, in Mark, arrive from Jairus house with news that Jairus daughter is dead, and presenting that statement as something Jairus said. Is Matthews treatment of this particular detail non-historical? Yes. But does that make it an error? By first-century standards, no; it makes it a summary. Matthew was not aiming for a strictly historical presentation; his goal is to write a literary portrait of Jesus. In the process, Matthew sometimes merely sketches the background of Jesus actions and sayings. This is one of those times. This resolution does not consist of a harmonization of the accounts; it is a result of readers appreciation of the nature of each Gospel as something more like a series of paintings and sketches than a series of photographs.
Second solution: when Jairus came to Jesus, Jairus was over-excited and began his request by saying that his daughter was dead, but then he said that his daughter was almost dead. Matthew recollects one statement, and Mark (recording Peters recollections) records the other.
Third solution: Jairus made his statement in Aramaic and used a phrase which was capable of meaning either that his daughter had just died, or that she was about to die. Suppose someone told a doctor, Help! My daughter is in the grip of death, but I know you can save her! -- does this person mean that his daughter has recently died, or that she is still alive but right at deaths door? Technically it is capable of either meaning. When putting the statement into Greek, Matthew emphasized one shade of meaning, which facilitated the abbreviation in his report, and Mark emphasized the other.
Fourth solution: Jairus stated, as Matthew says, that his daughter had just died. But underlying this statement was Jairus belief that his daughters soul was still lingering around. In other words, Jairus said that she was dead, but his concept of death was of something that could be fixed if one remedied it right away. (Sort of like in "The Princess Bride.") Matthew recorded his statement as-is, and Mark paraphrased it so as to convey what it would be understood to mean.
Yours in Christ,
Waterrock
