Why was Luuna on Baytril?
Was she drinking a lot before being on abx?
TBH I would discuss the situation with your Vet as whilst Panacur is relatively 'safe' it is never a good idea to just make assumptions as to what may be wrong with a Bun. The 'head-twitch' may be EC related but it may not. Just treating the symptomatic Bun is one thing but I would not want to be treating both Buns with Panacur for 6 weeks based on an assumption.
Also, there are other reason for excessive drinking apart from EC ( UTI, Bladder Sludge/Stones, Kidney/Liver problems, Dental problems) so it would be a good idea to get that checked out to
Good Luck
Janex