Do NOT recommend that she reach out to her “old buyers” to see if they need anything. That can be considered spam, and will get her account a warning or worse, banned. Once you deliver an order, let the buyer contact YOU if they need to, not the other way around.
Since you recently joined Fiverr, what likely is occurring is, when you listed your Gig, it got a boost being new, and now that period is over - so, your Gig is probably not getting the same exposure as it did when new. It has nothing to do with people vacationing through January.