Change the Experience rule to read:

Each Valkyrie shall have an Experience statistic, to be tracked in the GNDT. Each Valkyrie’s Experience statistic will start at 0. Whenever a Valkyrie wins a skirmish, she receives a number of Experience points equal to DICEX, where X is the Valkyrie’s Skirmish Rating. If a Valkyrie wins a skirmish with a Skirmish Rating of 0 or less, she receives 1 Experience point.  The Valkyrie that owned the Einherjar that was transfered to Loki has her experience reduced by 1 (this may result in negative experience), and all other Valkyries will increase their experience by 1.

A Valkyrie may rediuce her Experience by Y in order to raise one statistic, except Tinkering, of one of the Einherjar she has recruited by 1 point, where Y equals half of eleven more than the current value of the statistic to be raised [Y=1/2*(current value +11)] rounded up, as long as the Valkyrie has at least Y experience. No Valkyrie may raise an Einherjar’s statistic whose value is +10.