I think we could distinguish this case on several grounds:
a) This communication is a personal one unrelated to Rose's work. It is not as though Jack sent communication to a fax machine or email address where email will be monitored by a secretary, receptionist, etc at all times during business hours. I suggest that the rule in the Digilandmall.com case is more appropriate where the communication is part of the 'ordinary course of dealing' of the email/IP address to which it is sent. This is essentially what is being said in the obiter dicta in the Brimnes case as well. In that case it was expected that the receptionist would notice the fax within a matter of moments as indeed she was employed to do so.
b) The process in the digiland case was somewhat more 'automated'. The customer placed an order for a laser printer and received an automated acknowledgement shortly thereafter, with an order automatically being created in digilandmall's system.
c) The judgment in digiland actually states: "In accordance with s 15(1) of the ETA, acceptance would be effective the moment the offer enters that node of the network outside the control of the originator. There are, however, other sound reasons to argue against such a rule in favour of the recipient rule", and Rajah JC goes on to state in any case "In the absence of proper and full arguments on the issue of which rule is to be preferred, I do not think it is appropriate for me to give any definitive views in these proceedings on this very important issue."
d) There ought to be a big difference between wholesalers of printers and sellers of a single camper van. In the former case, barring mistakes such as what actually happened, the wholesalers envisage being able to meet any such orders for merchandise that come in. Furthermore, they may have systems in place to monitor their stock based on what has been ordered and remove such articles from their website as have been 'sold out'. In the latter case, the seller clearly only has one such camper van, and so anything that might lead to her potentially selling an arbitrarily large number of vans that she doesn't have should be looked at skeptically
e) In the absence of any clear authority, you might like to consider who it is fairer should 'bear the risk' of this type of thing happening. Is it more reasonable that Rose should be liable for breach of contract because she didn't check her email in the last few minutes before she left for work, or is it more reasonable that Jack should not be able to buy a camper van? Note that Jack could easily have confirmed his order by simply calling Rose as he had done previously (and in the real world rather than the stilted world of law problem questions, surely he would have done)?
In the final analysis your view may be correct but hopefully those are some things that you can consider whether or not are relevant to your essay.
(note that I'm only a 1st year law student as well so you have as much chance of being right as I do !)