Wacky Suggestion
OTOH, if you don't want to bother with recalculating the character, just leave them at the current level, but with a exp defict that they have to make up.
For example, assume that the character has 17,000 exp. After she gets raised she would be at 12,500 exp. The difference is 4500 exp. So, she has to earn 4500 exp before she can continue her progress towards 7th level. This way the character stays at 6th level, you don't have to figure out lost skills, hit points, etc.
Another wacky idea is to instead leave her at 17,000, but everytime she earns exp. give half to her character and half to paying off the deficit. That way the character still has the feel of progressing, but only slower.
Another possiblity, but is definitely more towards a house rule. Everytime a character dies and is raised they take a permanent 5% exp penalty.